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    UNIVERSITY OF KANSAS PUBLICATIONS
    MUSEUM OF NATURAL HISTORY

    Volume 13, No. 7, pp. 323-348, pls. 21-24, 2 figs.

    February 10, 1961




    Geographic Variation
    In the North American Cyprinid Fish,
    Hybopsis gracilis

    BY

    LEONARD J. OLUND AND FRANK B. CROSS


    UNIVERSITY OF KANSAS
    LAWRENCE
    1961


    UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

    Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
    Robert W. Wilson


    Volume 13, No. 7, pp. 323-348, pls. 21-24, 2 figs.
    Published February 10, 1961


    UNIVERSITY OF KANSAS
    Lawrence, Kansas


    PRINTED IN
    THE STATE PRINTING PLANT
    TOPEKA, KANSAS
    1961

    [Illustration]

    28-5871




Geographic Variation
In the North American Cyprinid Fish,
Hybopsis gracilis

BY

LEONARD J. OLUND AND FRANK B. CROSS




CONTENTS


                                                     PAGE

    INTRODUCTION                                      325

    METHODS, MATERIALS, AND ACKNOWLEDGMENTS           326

    DESCRIPTION OF THE SPECIES HYBOPSIS GRACILIS      327
        _Hybopsis gracilis gracilis_                  328
        _Hybopsis gracilis gulonella_                 330

    INTRASPECIFIC VARIATION                           333

    NATURAL HISTORY                                   334
        _Habitat_                                     334
        _Associated Species_                          336
        _Food_                                        338
        _Spawning Season_                             338

    DISCUSSION                                        340

    LITERATURE CITED                                  343




INTRODUCTION


The flathead chub, _Hybopsis gracilis_ (Richardson), occurs in the
Plains Region of Canada and the United States, in four major drainage
systems: Mackenzie River, which discharges into the Arctic Ocean;
Saskatchewan River, which discharges into Hudson Bay via Nelson River;
and Missouri-Mississippi System and Rio Grande, both draining into the
Gulf of Mexico. Each of these systems is occupied in part only. In the
Mackenzie Basin, _H. gracilis_ has been reported as far north as Fort
Good Hope (Walters, 1955:347). Flathead chubs occur in the Saskatchewan
Basin from Alberta eastward to Lake Winnipeg, Manitoba, but have not
been found in other streams that flow into Lake Winnipeg (Red River,
Brokenhead River and Whitemouth River) nor in Nelson River downstream
from Lake Winnipeg. In the Missouri Basin the species occurs more or
less continuously from the high plains adjacent to the Rocky Mountains
in Montana and Wyoming down the mainstream of the Missouri River to its
mouth, and down the mainstream of the Mississippi River as far as
Barfield, Arkansas, but not to the Gulf. The species probably attains
its greatest abundance in the Missouri Basin, but it is scarce or absent
in tributaries north and east of the Missouri mainstream, in the South
Platte Basin, and in the central part of the Platte River in Nebraska.
The flathead chub is unknown in the Mississippi Basin above the mouth of
the Missouri River, and in the Ohio River Basin above its mouth. In the
Arkansas River Basin, records are restricted to (1) the headwaters and
tributaries of the Arkansas River from eastern Colorado downstream as
far as Garden City, Kansas, (2) the Cimarron River at Kenton, Cimarron
County, Oklahoma, and (3) the South Canadian River and tributaries from
northeastern New Mexico eastward as far as Norman, McClain County,
Oklahoma, but rarely there. Thus, the range in the Arkansas Basin seems
to consist of three isolated segments. Likewise, isolated populations
exist in the Rio Grande System, where flathead chubs are confined to the
upper parts of the Rio Grande and Pecos basins, above the confluence of
the Rio Grande and Pecos Rivers. Records resulting from introductions
have been reported for the Gila River by Koster (1957:62) and from the
Snake River, Wyoming, by Simon (1946:72).

Six names apply to the flathead chub, the earliest of which is _Cyprinus
gracilis_ Richardson (1836:120). Other names have sometimes been
accepted as applicable to valid species and/or subspecies, but usage,
diagnoses, and stated ranges have been confusingly inconsistent. For
most of the past 100 years, _Platygobio_ Gill has been recognized as the
appropriate generic name for the flathead chub, but Bailey (1951:192)
places _Platygobio_ and other nominal genera of barbeled minnows having
short guts, protractile premaxillae, and four teeth (primary row) in the
single genus _Hybopsis_ (Agassiz, 1854). Strangely, the orthotype of
_Hybopsis_, _H. gracilis_ Agassiz, is a junior synonym of _H. amblops_
(Rafinesque) (Hubbs and Ortenburger, 1929b:66) and is a younger name
than _C. gracilis_ Richardson.

The purpose of this paper is to redescribe the species and to make known
its pattern of geographic variation. Natural history will also be
considered, as will habitat, food habits, and breeding season.




METHODS, MATERIALS AND ACKNOWLEDGMENTS


Ten meristic characters and seventeen measurements of body-parts (the
latter expressed as proportions of standard length) have been analyzed.
They are: number of rays in the dorsal, anal, caudal, pectoral and
pelvic fins; number of scales in the lateral line, before the dorsal
fin, around the body and around the caudal peduncle; number of
vertebrae; body-depth, depth of caudal peduncle, length of caudal
peduncle, predorsal length, length of depressed anal and dorsal fins,
length of pectoral and pelvic fins, head-length, head-depth,
head-width, snout-length, postorbital length of head, length of orbit,
interorbital width, length of upper jaw and width of gape.

Counts and measurements were made as described by Hubbs and Lagler
(1958), with the exception of scales before the dorsal fin, which were
counted as the number of vertical scale-rows between the upper margin of
the opercular cleft and the origin of the dorsal fin. Vertebral counts,
made from roentgenograms, excluded vertebrae in the Weberian complex
(presumably always four) but included the hypural vertebra.

Counts and measurements were made on series (usually ten fish) from
localities throughout the range. To minimize effects of allometric
growth, the fish were divided into several length-groups prior to
analysis of proportional measurements: 30-50mm, 50-70mm, 70-100mm,
100-150mm, 150-200mm and 200mm standard length and over. The majority of
specimens examined were 70-100mm in standard length.

Specimens were obtained from the following institutions: University of
Alberta (abbreviated UA in the text); Museum of Zoology, University of
Michigan (UMMZ); University of Missouri (UM); Montana State College
(MSC); University of Oklahoma Museum of Zoology (UOMZ); University of
Saskatchewan; Royal Ontario Museum, Division of Zoology, Toronto (ROMZ);
University of Wyoming (WU); Museum of Natural History, University of
Kansas (KU). Specimens examined are listed in the accounts of the
subspecies.

We are grateful to D. A. Boag, Reeve M. Bailey, Arthur L. Witt, C. J. D.
Brown, Carl Riggs, F. M. Atton, W. B. Scott, and George Baxter, all
staff-members of the institutions listed in the immediately preceding
paragraph, for placing specimens at our disposal. Mr. William Peters
analyzed the contents of stomachs of specimens that were used for study
of the food habits. Mr. Artie L. Metcalf assisted in collecting
specimens. Drs. Kenneth B. Armitage and E. Raymond Hall offered valued
suggestions in connection with the preparation of the manuscript.




DESCRIPTION OF THE SPECIES


=Hybopsis gracilis= (Richardson)

Flathead Chub

(Synonymy under accounts of subspecies)

_Description._--Pharyngeal teeth 2,4-4,2, hooked; dorsal fin of
moderate size, falcate, first principal ray longest, extending beyond
posterior rays in depressed fin, its origin usually slightly in front
of insertion of pelvic fin, approximately equidistant from tip of snout
and base of caudal fin, rays 8, rarely 9; pectoral fin strongly
falcate, rays 14-20, usually 16-18; pelvic rays 8, rarely 9; anal fin
falcate, rays 8, rarely 9; caudal rays 19, rarely 20.

Body slightly compressed, nearly terete; head-length 23.1-28.8 per cent
of standard length; head broad and flattened, snout subconical,
premaxillae protractile, upper lip not medially expanded; mouth
subterminal, nearly horizontal, large; a single pair of terminal
maxillary barbels; orbit usually 5-7 per cent of standard length;
lateral line slightly decurved; intestine short, peritoneum silvery.

Color brown or olivaceous dorsally, silver or creamy white ventrally,
without distinctive markings; dusky lateral band evident in preserved
specimens.

Taste-buds present on membrane between first and second principal rays
of all fins, and on first to sixth interradial membranes of pectoral
fin. On the caudal fin, taste buds between first and second principal
rays of upper and lower lobes, though present, are less well developed
than on other fins. Moore (1950:88) states that taste buds are numerous
on the barbels, cheeks, lips, chin, snout, opercles and branchial
membranes, and are present in decreasing numbers over the body.

Nuptial tubercles of male minute and densely scattered over top of head
and snout; usually present on pectoral rays 1-8, weak when present on
rays beyond the eighth, never found beyond the eleventh ray; minute
tubercles usually found on dorsal, pelvic and anal fins, rarely on lower
scales of caudal peduncle; predorsal scales have a fine peripheral row
of tubercles.


=Hybopsis gracilis gracilis= (Richardson)

(Plate 22)

  _Cyprinus (Leuciscus) gracilis_ Richardson, 1836:120 and Pl. 78
    (original description; Saskatchewan R. at Carlton House).

  _Coregonus angusticeps_ Cuvier and Valenciennes, 1848:534
    (original description; Saskatchewan R.).

  _Pogonichthys communis_ Girard, 1856:188 (in part; original
    description); Girard, 1858:247 and plate 55 (in part;
    characters; synonymy); Suckley, 1860:361 (Milk R.); Cope,
    1879:440 (Fort Benton, Mo. R.; Judith R.).

  _Platygobio gracilis_, Jordan and Gilbert, 1882:219 (in part;
    characters; synonymy); Graham, 1885:74 (Kansas R.; synonymy);
    Jordan, 1885:29 (records); Jordan and Meek, 1886:13 (Mo. R., St.
    Joseph, Mo.); Meek, 1892:245 (characters; Mo. R., Sioux City,
    Iowa); Eigenmann, 1895:111 (Craig; Poplar; Brandon; Medicine
    Hat); Meek, 1895:137 (Platte R., Fremont, Neb.); Evermann and
    Cox, 1896:412 (in part; habitat; synonymy); Jordan and Evermann,
    1896:326 (in part; characters; synonymy); Thompson, 1898:214
    (Brandon; Saskatchewan R.); Evermann and Goldsborough, 1907:98
    (records from Canada); Forbes and Richardson, 1920:170
    (characters; habitat; synonymy; records from Illinois; but Fig.
    45 is _Hybopsis meeki_ Jordan and Evermann, not _H. gracilis_);
    Hankinson, 1929:446 (records from North Dakota); Jordan, 1929:76
    (in part; characters); Jordan, Evermann and Clark, 1930:136 (in
    part; synonymy); Churchill and Over, 1933:45 (characters; food;
    habitat; spawning; records from South Dakota); O'Donnel,
    1935:481 (Ohio R., Cairo, Ill.; Miss. R., Chester, Ill.); Hinks,
    1943:57 (records from Canada); Clemens, _et al._, 1947:17
    (records from Saskatchewan); Dymond, 1947:19 (distribution in
    Canada); Rawson, 1951:208 (Great Slave Lake; Mackenzie R.);
    Shoemaker, Pickering and Durham, 1951:84 (Miss. R., Cates, Tenn.;
    Miss. R., between Hickman and Barfield, Ark.); Wynne-Edwards,
    1952:18 (distribution in Canada); Miller and Paetz, 1953:47
    (Peace R. at town of Peace River); Walters, 1955:347
    (distribution in Canada; dispersal into Canada); Keleher,
    1956:265 (Saskatchewan R., Manitoba); Lindsey, 1956:771
    (distribution in Canada); Keleher and Kooyman, 1957:110 (Kelsey
    Lake, Manitoba); Lindsey, 1957:657 (Laird and Peace drainages,
    British Columbia); Scott, 1958:16 (distribution in Canada);
    Slastenenko, 1958:7 (distribution in Canada).

  _Platygobio pallidus_ Jordan and Gilbert, 1882:220 (original
    description; Ohio R., Cairo, Ill.); Jordan and Evermann,
    1896:326 (characters; synonymy; Ohio R., Cairo, Ill.); Jordan,
    Evermann and Clark, 1930:136 (Ohio R., Cairo, Ill.; synonymy).

  _Platygobio gracilis communis_, Simon, 1946:71 (in part;
    characters; food; habitat; spawning); Moore, 1950:87 (habitat;
    sense organs).

  _Hybopsis gracilis communis_, Bailey, 1951:192 (record from Iowa;
    key); Harlan and Speaker, 1951:75 (characters; distribution in
    Iowa); Hubbs, 1951:9 (habitat; Miss. R.); Harrison and Speaker,
    1954:516 (habitat); Personius and Eddy, 1955:42 (habitat; Little
    Mo. R.).

  _Hybopsis gracilis_, Cleary, 1956:271 (record from Iowa;
    distributional map); Bailey, 1956:332 (record from Iowa; key);
    Harlan and Speaker, 1956:90 (characters; distribution in Iowa);
    Eddy, 1957:111 (in part; characters; key); Moore, 1957:110 (in
    part; key); Underhill, 1959:100 (Vermillion R., South Dakota).

_Diagnosis._--Post-Weberian vertebrae 40-42, usually 41-42; lateral
line scales 50-56; pectoral rays 15-20, usually 17 or more; head-depth
12.3-15.1 per cent of standard length, usually 14.7 per cent or less.
See Figs. 1 and 2.

_Other characters._--Circumference scale-rows 31-42; predorsal
scale-rows 20-29; size large, as much as 246 mm standard length (see
Fig. 1 of Pl. 24); head-length 23.4-27.4 per cent of standard length,
usually 25.5 per cent or less; postorbital length of head 10.9-13.9 per
cent of standard length, usually 12.5 per cent or less; predorsal length
46.0-51.7 per cent of standard length; orbit 5.1-6.8 per cent of
standard length; prepelvic length 46.6-52.2 per cent of standard length;
caudal peduncle length 17.2-22.1 per cent of standard length.

_Range_ (Plate 21).--Mackenzie Basin south from Fort Good Hope;
Saskatchewan Basin east to Lake Winnipeg; mainstream of Missouri River
and Mississippi River south to Barfield, Arkansas; intergrading with _H.
g. gulonella_ in upper Missouri Basin and lower parts of major
tributaries to Missouri River in Nebraska and Kansas.

_Specimens examined._--Below are listed museum numbers, number of
specimens (in parentheses), localities, and year of collection.
Collections marked with asterisk (*) are intergrades more closely
resembling _H. g. gracilis_ than _H. g. gulonella_. Records from
literature are cited in the synonymy.

ALBERTA: UA (6), Milk R. at town of Milk River, 1950; UA (3), Athabasca
R. at Fort McMurray, 1955; UA (1), Red Deer R. at Steveville, 1952; UA
(2), Peace R. at town of Peace River, 1952; UA (11), Peace R. at
Dunvegan, 1956; UA (2), Simonette R. tributary to Smoky R., date
unknown; ROMZ 17704 (1), Milk R. W town of Milk River, 1955.

ARKANSAS: UMMZ 128573 (5), Mississippi Co., Mississippi R., 1939.

ILLINOIS: UMMZ 134799 (146), Mississippi R. at Grand Tower, 1936; UMMZ
147045 (8), Mississippi R. at Cairo, 1944.

KANSAS: KU 1234 (173), Leavenworth Co., backwater of Missouri R. near
Corral Cr., 1940; * KU 1814 (1), Douglas Co., floodpool of Kansas R.,
below Lakeview, 1951; * KU 1825 (1), Douglas Co., floodpool of Kansas
R., 1951; * KU 1841 (56), Douglas Co., Kansas R. at Lawrence, 1951; * KU
1898 (6), Douglas Co., floodpool of Kansas R., 1951; * KU 1911 (5),
Douglas Co., floodpool of Kansas R., 1951; * KU 1928 (2), Jefferson Co.,
floodpool of Kansas R., 1951; KU 3850 (30), Atchison Co., Missouri R.,
1957; * KU 4377 (2), Douglas Co., Kansas R. at Lawrence, 1958; * KU 4655
(2), Douglas Co., Kansas R. at Lawrence, 1959.

MANITOBA: ROMZ 13834 (1), Kelsey Lake, 25 miles east of the Pas, no
date; ROMZ 14500 (25), Saskatchewan R. at the Pas, 1947; ROMZ 16325 (1),
Lake Winnipeg, no date.

MISSOURI: UMMZ 147126 (130), Mississippi R. at Cliff Cave, 1944.

MONTANA: * MSC 1878 (36), Carbon Co., Elbow Cr., 1957; * MSC 1943 (11),
Phillips Co., Frenchman Cr., 1957; * MSC 2021 (10), Pondora Co., Marias
R., 1955; * MSC 2022 (4), Lewis and Clark Co., Missouri R. below Holter
Dam, 1948; * MSC 2052 (6), Gallatin Co., Missouri R. near Trident, 1948;
* MSC 3074 (3), Custer Co., Hardy Reservoir, 1952; UMMZ 94146 (34), near
mouth of Powder R., 1926.

NEBRASKA: * KU 4158 (9), Holt Co., Niobrara R. 6 mi. N Midway, 1958; *
UM (field no. 59-81) (56), Butler Co.-Colfax Co. line, Platte R. 1.5 mi.
S Schuyler, 1959; * UM (field no. 59-74) (5), Dodge Co., Platte R. 1 mi.
S North Bend, 1959; UMMZ 134826 (46), Otoe Co., Missouri R. 1.5 mi. E
Minersville, 1940; UMMZ 134799 (67), Cass Co., Missouri R., 1940; UMMZ
135341 (43), Knox Co., Missouri R. 2 mi. NE Niobrara, 1940; UMMZ 135818
(95), Thurston Co., Missouri R. NE Macy, 1941.

NORTHWEST TERRITORY: ROMZ 13627 (1), Great Slave Lake, no date; ROMZ
13628 (1), Great Slave Lake, no date.

SASKATCHEWAN: * ROMZ 3885 (2), Sucker Cr., trib. Cypress Lake, 1927;
ROMZ 14368 (2), South Saskatchewan R. at Yorath Island, 1941; ROMZ 16620
(5), South Saskatchewan R. at Saskatoon, 1953; KU 5126 (5), South
Saskatchewan R. at Birson Ferry, 1957; KU 5127 (3), South Saskatchewan
R. at Leader, 1957; KU 5128 (2), North Saskatchewan R. at Cecil Ferry,
1957; KU 5129 (1), South Saskatchewan R. at Clarkboro Ferry, 1957.

SOUTH DAKOTA: * KU 4961 (9), Haakon Co., Bad R. at Midland, 1959; * KU
4963 (17), Washabaugh Co., White R. 6 mi. SW Belvidere, 1959; * UMMZ
120362 (168), White R. 6.5 mi. S Kadoka, 1934; * UMMZ 127484 (11), Todd
Co., Little White R., 1934; UMMZ 127488 (29), Charles Mix Co., Missouri
R., 1934; * UMMZ 127678 (32), Cheyenne R., E Wasta, 1939; UMMZ 166762
(21), Hughes Co., Missouri R. 3 mi. NE Pierre, 1952; * UMMZ 166803 (91),
Harding Co., Little Missouri R. at Camp Crook, 1952; UMMZ 166845 (121),
Carson Co.-Walworth Co. line, Missouri R. 2.5 mi. N Mobridge, 1952; UMMZ
166985 (61), Yankton Co., Missouri R. at Yankton, 1952.

WYOMING: * WU 2073 (6), Washakie Co., Big Horn R. at Worland, 1956.


=Hybopsis gracilis gulonella= (Cope)

(Plate 23)

  _Pogonichthys communis_ Girard, 1856:188 (in part; original
    description); Girard, 1858:247 (in part; characters; synonymy);
    Cope and Yarrow, 1875:653 (characters; Pueblo, Colo.).

  _Pogonichthys (Platygobio) gulonellus_ Cope, 1864:277 (original
    description; near Bridger's Pass, Wyo.).

  _Platygobio gulonellus_ Cope, 1865:85 ("Platte R., near Fort
    Riley" [Fort Riley is on Kansas R., not Platte R.; Cope's
    specimens probably are from Platte drainage, on basis of known
    distributions of other species reported]).

  _Ceratichthys physignathus_ Cope and Yarrow, 1875:651 (original
    description; Arkansas R., Pueblo, Colo.).

  _Platygobio communis_, Gill, 1876:408 (characters; Platte Valley;
    Green River, Utah [the latter probably erroneous]).

  _Couesius physignathus_, Jordan and Gilbert, 1882:219 (characters;
    synonymy; Arkansas R., Pueblo, Colo.); Jordan, 1885:29
    (records).

  _Platygobio gracilis_, Jordan and Gilbert, 1882:219 (in part;
    characters; synonymy); Cragin, 1885:109 (Garden City, Kans.);
    Gilbert, 1885:98 (Garden City, Kans.); Jordan, 1885:29
    (records); Evermann and Cox, 1896:412 (in part; habitat;
    synonymy); Jordan and Evermann, 1896:326 (in part; characters;
    synonymy); Ortenburger and Hubbs, 1927:125 (Canadian R., Norman,
    Okla.); Hubbs, 1927:75 (parasites; teratology; records from New
    Mexico); Hubbs and Ortenburger, 1929a:28 (S. Canadian R.,
    Durham, Okla.); Jordan, 1929:76 (in part; characters); Jordan,
    Evermann and Clark, 1930:136 (in part; synonymy).

  _Platygobio physignathus_, Jordan and Evermann, 1896:325
    (characters; synonymy; records from upper Arkansas R.); Ellis,
    1914:62 (characters; synonymy; records from Colorado);
    Cockerell, 1927:123 (distribution in Colorado); Jordan, Evermann
    and Clark, 1930:136 (synonymy; records from upper Arkansas R.).

  _Platygobio gracilis communis_, Simon, 1946:71 (in part;
    characters; food; habitat; spawning).

  _Platygobio gracilis gulonellus_, Simon, 1946:72 (characters;
    records from Wyoming; Arkansas R.).

  _Platygobio gracilis:_ _communis_ × _gulonellus_, Simon, 1946:92
    (North Platte R., Neb.-Wyo. line).

  _Platygobio gracilis physignathus_, Moore, 1950:87 (habitat; sense
    organs).

  _Hybopsis gracilis communis_, Beckman, 1952:50 (characters; food;
    habitat); Cross, Dalquest and Lewis, 1955:222 (records from
    Texas).

  _Hybopsis gracilis physignathus_, Beckman, 1952:50 (characters;
    habitat).

  _Hybopsis gracilis_, Eddy, 1957:111 (in part; characters; key);
    Koster, 1957:61 (characters; habitat; spawning; food); Moore,
    1957:110 (in part; key); Smith, 1958:177 (fossil record; Doby
    Springs, Okla.).

_Diagnosis._--Post-Weberian vertebrae 36-38, rarely 39; lateral line
scales 42-54, usually less than 50; pectoral rays 14-19, usually fewer
than 17; head-depth 13.5-18.0 per cent of standard length, usually 14.8
per cent or more. See Figures 1 and 2.

_Other characters._--Circumference scale-rows 30-40, slightly fewer than
in _H. g. gracilis_; predorsal scale-rows 17-27, somewhat fewer than in
specimens from Canada, but much the same as specimens from the
Missouri-Mississippi system; size small, rarely as much as 130 mm
standard length (Fig. 1 of Pl. 24); head-length 24.0-28.0 per cent of
standard length, usually more than 25.5 per cent; postorbital length of
head 11.2-14.4 per cent of standard length, usually more than 12.5 per
cent (both characters illustrate the larger head of _H. g. gulonella_);
predorsal length 46.4-52.7 per cent of standard length, longer than in
the other subspecies; orbit 5.0-6.6 per cent of standard length;
prepelvic length 47.4-53.7 per cent of standard length, longer than in
_H. g. gracilis_; caudal peduncle length 17.1-22.7 per cent of standard
length, essentially the same in both subspecies.

The label on types of this subspecies, in the Academy of Natural
Sciences of Philadelphia, states merely "near Bridger's Pass, Wyo.,
Expedition of 1856, Dr. W. A. Hammond" (letter from Dr. James Böhlke to
Cross, dated Jan. 27, 1960). Dr. Hammond was a surgeon who also
collected scientific specimens, assigned to an expedition under the
command of Lt. F. T. Bryant. Bryant's log is recorded in the Proceedings
of the 35th Congress (1858:455-481). The site at which these specimens
were taken cannot be ascertained from the log, but study of it is
helpful in indicating the probable locations.

The expedition left Fort Riley on June 21, 1856, on the following route:
up Republican River; across to Fort Kearney on Platte River; west along
Platte River to S. Platte River; up S. Platte River to Pole (Lodgepole)
Creek; Pine-Bluffs (Neb.-Wyo. line); across East Fork to West Fork of
Laramie River; Cooper's Creek; West Fork of Medicine Bow; Pass Creek and
down canyon of Pass Creek; across N. Platte River; up Sage Creek; on
August 15, camped on Muddy Creek, tributary to Green River (first record
of fish, trout); back to Sage Creek; August 19-21, camped on island in
North Platte River; to Pass Creek; Elk Creek; west branch of Medicine
Bow; Aspen Creek; West Fork of Laramie River; August 29, to East Laramie
River where a large supply of fish was caught; tributary of Cache la
Poudre then downstream to mouth of this river; down South Platte River
past mouth of Crow Creek and Beaver Creek; left South Platte River 14
miles below mouth of Beaver Creek, toward Republican River; down Rock
Creek to Arikaree; down Arikaree to Republican River and down the
Republican to Fort Riley.

Mention is made of fish only twice in the entire log. We doubt that
Muddy Creek or the East Laramie River is the type locality of _P.
gulonellus_, because the flathead chub has not since been found in
either of these streams. The most likely collection site for _P.
gulonellus_ is the North Platte River near the mouth of Sage Creek, in
what is now Carbon County, Wyoming, where the expedition was camped for
three days. This species is known to occur in the North Platte River,
and since the type locality is reported as "near Bridger's Pass" this is
the probable location.

_Range_ (Plate 21).--Upper mainstream and tributaries of Rio Grande,
Pecos, Arkansas and North Platte Rivers; isolated populations in
tributaries of the upper Missouri River.

_Specimens examined._--Below are listed museum numbers, number of
specimens (in parentheses), localities and year of collection. Series
marked by asterisks (*) are intergrades tending toward _H. g.
gulonella_. Literature reports are cited in the synonymy.

COLORADO: KU 4742 (162), Bent Co., Purgatoire R. at Las Animas, 1959; KU
4748 (105), Pueblo Co., Arkansas R. at west edge of Pueblo, 1959; KU
4758 (50), Fremont Co., Arkansas R. at Florence, 1959; KU 4769 (64),
Fremont Co., Beaver Cr., 1959.

KANSAS: KU 2648 (2), Finney Co., Arkansas R., 1958; KU 2858 (13), Finney
Co., Arkansas R. at Garden City, 1951; KU 3964 (12), Kearney Co.,
Arkansas R., 1958; * KU 4041 (2), Cheyenne Co., Republican R., 1958; KU
4732 (30), Hamilton Co., Arkansas R. at Kendall, 1959; * KU 4868 (1),
Kansas-Nebraska line, Republican R. 1.5 mi. S. Hardy, 1959.

MONTANA: * MSC 1960 (8), Powder River Co., E. Fork of Powder R., 1957;
MSC 2010 (64), Dawson Co., Redwater R., 1957.

NEBRASKA: * KU 2140 (2), Dawson Co., Platte R., at Gothenburg, 1931; *
KU 4863 (20), Furnas Co., Republican R. at Cambridge, 1959; * UM (field
no. 59-49) (74), Scotts Bluff Co., North Platte R. at Morrill, 1959; *
UMMZ 133918 (17), Dixon Co., Logan Cr., 1939; * UMMZ 134813 (31), North
Platte R., Neb.-Wyo. line, 1941; * UMMZ 135084 (14), Harlan Co., Beaver
Cr. 0.25 mi. S Stamford, 1940; * UMMZ 135200 (41), Scotts Bluff Co.,
North Platte R. 1 mi. SE Henry, 1940; * UMMZ 135280 (59), Cherry Co.,
Niobrara R. 3 mi. SE Valentine, 1940; * UMMZ 135700 (25), Buffalo Co.,
South Loup R. 8 mi. N Miller, 1941; * UMMZ 135778 (54), Thurston Co.,
Logan Cr. 2.5 mi. W Pender, 1941; * UMMZ 135786 (25), Dixon Co., Logan
Cr. 0.5 mi. NW Wakefield, 1941.

NEW MEXICO: KU 4219 (50), Colfax Co., Cimarron Cr. at Springer, 1958; KU
4235 (19), Mora Co., Sapello Cr. near Sapello, 1958; KU 4245 (157),
Bernalillo Co., Rio Grande 12 mi. S Bernalillo, 1958; KU 4255 (22), Rio
Arriba Co., Rio Grande at Velarde, 1958; KU 4266 (53), Sandoval Co., Rio
Grande 2 mi. N Cochiti Pueblo, Marcelino Baca bridge, 1958; KU 4269
(91), San Miguel Co., Pecos R., 3 mi. S Pecos, 1958; KU 4274 (25),
Sandoval Co., Jemez R. at Jemez Canyon Dam, 1958; KU 4294 (113),
Guadalupe Co., Pecos R. 3 mi. N. Dilia, 1958; UMMZ 94897 (146), Pecos R.
at San Tuan, 1926; UMMZ 94898 (1), Pecos R. at San Juan, 1926; UMMZ
118209 (68), Sapello Cr. at Sapello, 1937; UMMZ 133131 (7), Pecos R.
0.5 mi. N Santa Rosa, 1940; UMMZ 133136 (1), Rio Grande at Albuquerque,
1940.

OKLAHOMA: KU 2329 (1), Cleveland Co.-McClain Co. line, S. Canadian R.,
1952; UOMZ 26355 (10), Cimarron Co., Cimarron R. 2 mi. N. Kenton, 1957;
UOMZ 5917 (2), Cleveland Co., S. Canadian R. S Norman, 1925.

TEXAS: KU 3409 (18), Hemphill Co., Canadian R. at town of Canadian,
1955.

WYOMING: WU 2084 (4), Platte Co., N. Platte R. at Glendo, 1956; WU 2095
(3), Converse Co., N. Platte R. at Douglas, 1956; UMMZ 104064 (58), N.
Platte R. below Guernsey Dam, 1937; * UMMZ 114642 (7), drainage ditch in
Wind R. drainage, 1936; * UMMZ 114644 (20), drainage ditch at Riverton,
1936; * UMMZ 127518 (63), Weston Co., Beaver Cr., 1934; * UMMZ 127681
(20), Big Horn Co., Big Horn R. tributary, 1939; * UMMZ 136488 (9),
Crook Co., Belle Fourche R. 15 mi. N Devil's Tower, 1941; * WU 2122 and
two uncatalogued series at WU (13), Belle Fourche R., no precise
locality or date; UMMZ 159969 (14), Natrona Co., N. Platte R. 2 mi. E
Casper, 1950.




INTRASPECIFIC VARIATION


Two subspecies of _H. gracilis_ are recognized by us: one northern and
eastern, characteristically inhabiting large rivers (_H. g. gracilis_),
and one southern and western, characteristically inhabiting small
streams (_H. g. gulonella_). Other scientific names that have been
applied to this fish in the past are listed in the synonymy.

_H. g. gulonella_ is a chubby, deep-bodied fish, whereas _H. g.
gracilis_ is long and slender. The head of the creek subspecies is
deeper and longer than that of _H. g. gracilis_, being rounded
anteriorly when seen in sideview. The head of the large-river subspecies
is acutely wedge-shaped in profile. _H. g. gracilis_ has a larger orbit
than _H. g. gulonella_. Fins of _H. g. gracilis_ are more strongly
falcate than those of the other subspecies. _H. g. gracilis_ has a
greater number of lateral line scales, pectoral rays and post-Weberian
vertebrae than the creek subspecies. The large-river subspecies attains
much larger size than does the creek subspecies (Plate 24). Except in
areas of intergradation, complete separation of the two subspecies can
be made on the basis of lateral line scales, pectoral rays,
post-Weberian vertebrae and head-depth. The regressions of head-depth on
standard length in _H. g. gracilis_ from the Saskatchewan River (several
localities) and in _H. g. gulonella_ from Beaver Creek, Arkansas River
Drainage (KU 4769) are shown in Plate 24. Although values for the
largest specimens of _H. g. gracilis_ are omitted from Plate 24, the
regression remains essentially linear to standard lengths of
approximately 250 mm. On the basis of head-depth alone, separation of
the two subspecies is possible in specimens larger than 40 mm. Similar
results were obtained by using the regression of postorbital length on
standard length, and could have been obtained by using other
proportional measurements.




NATURAL HISTORY


_Habitat_

The species inhabits alkaline streams with shifting sand bottoms where
the waterlevel fluctuates considerably with heavy rains and melting
snow. The flathead chub is found in silty water and often is the
predominant species in streams that have high turbidity. The remarkable
ability of this fish to withstand exceedingly high turbidity is
illustrated by its predominance in the Little Missouri River, which has
an average concentration of suspended silt two and one-half times that
of the Missouri River at Kansas City (Personius and Eddy, 1955:42).

[Illustration: FIGURE 1. Graphic analysis of lateral line scales,
pectoral rays and post-Weberian vertebrae in _Hybopsis gracilis_.
In each symbol, horizontal line = range, vertical line = mean,
open rectangle = one standard deviation on each side of mean, black
rectangle = twice the standard error on each side of mean.

_H. g. gracilis_ is found in large rivers throughout its range,
occasionally migrating into smaller streams, especially in the spawning
season. It prefers the main channel of rivers in moderate to strong
current. All series examined are from elevations lower than 3,000 feet.

Numbers to left of symbols = number of specimens examined from that
locality; combined collections indicated by brackets. The dash-lines
represent drainage patterns of rivers in which this species occurs.]

_H. g. gulonella_ occupies small rivers and creeks, preferring pools
with moderate currents. In fall, dense concentrations of this subspecies
have been found in small pools, where brush, driftwood or other debris
deflects the current and prevents filling with drifting sand. Hundreds
of flathead chubs were collected in such pools in the Purgatoire and
Arkansas rivers. Specimens were also collected with ease in Beaver
Creek, Colorado, from pools with murky water and slight flow, over
bottoms of gravel and bedrock. No brush or other debris was near the
pools. In each case the streams carried little water, although they
undoubtedly carry greater volumes of water in spring and early summer
after rains and spring thaws. The preferred bottom-type for this
subspecies seems to be gently shifting sand.

_H. g. gulonella_ is found in warm-water streams, whereas _H. g.
gracilis_ occurs in cooler water. The southwestern subspecies was taken
in August in the Mora River drainage at Sapello (temperatures above 80°
F.) but not at Mora (temperatures below 70° F.). In the Purgatoire
River, a thriving population was found where the water temperature was
92° F., on September 6, 1959. In the Arkansas and Pecos rivers and the
Rio Grande this subspecies is most abundant below the mountainous parts
of the stream-courses, but at elevations higher than 4,000 feet on the
plains.


_Associated Species_

[Illustration: FIGURE 2. Graphic analysis of head-depth, postorbital
length of head and predorsal length of _Hybopsis gracilis_, expressed
as thousandths of standard length. Numbers in parenthesis = number
of specimens examined from each locality. In each symbol, horizontal
line = range, vertical line = mean, open rectangle = one standard
deviation on each side of mean, black rectangle = twice the standard
error on each side of mean. The dash-lines represent drainage patterns
of rivers in which this species occurs. All measurements are of
specimens 70 to 100 mm in standard length.]

In the Pecos and Arkansas basins, species commonly taken with _H. g.
gulonella_ are _Catostomus commersonnii_, _Hybognathus placita_,
_Notropis lutrensis lutrensis_, _Notropis stramineus missuriensis_,
_Pimophales promelas_, and _Campostoma anomalum plumbeum_. The only
spiny-rayed fishes that we have found with _H. g. gulonella_ are
_Lepomis cyanellus_ and _L. humilis_, both of which are scarce.
Associates of _H. g. gracilis_ include the same species, plus other
ostariophysan fishes such as species of _Carpiodes_, _Ictiobus_, and
silt-adapted species of _Hybopsis_ and _Notropis_.

We failed to find the flathead chub at any of 11 localities in the South
Platte drainage, where we collected in September, 1959. Dr. George
Baxter, of the Department of Zoology, University of Wyoming, told
us that he has never found _H. gracilis_ in that drainage. The fauna
of the South Platte includes _Catostomus catostomus_, _Semotilus
atromaculatus_, _Hybopsis biguttata_, _Hybognathus hankinsoni_,
_Notropis cornutus frontalis_, _Etheostoma nigrum_ and _E.
exile_--species rarely if ever found with _H. gracilis_.

Ecologically, _H. g. gulonella_ seems to be the counterpart of
_Semotilus atromaculatus_ in streams where the latter species is absent.
Observations of _H. g. gulonella_ in the Purgatoire River indicated
that loosely-organized groups of flathead chubs congregated one to four
inches above the bottom of pools, and near or under protective cover
such as roots of vegetation or debris lodged against shore. Individuals
moved about independently within the group (rather than as schools), and
occasionally rose to the surface, perhaps for food.


_Food_

The flathead chub is chiefly carnivorous, but its food includes some
aquatic vegetation (Table 1). Most organisms found in specimens (both
subspecies) were terrestrial insects (Coleoptera, Diptera, Orthoptera);
all insects were adult stages, except those designated as larvae in
Table 1. Roundworms probably were parasites, rather than food.

Hubbs (1927:76) states that the food of young flathead chubs that were
obtained from the Arkansas River System in New Mexico consisted "almost
entirely of crustaceans (small ostracods and cladocerans to the
exclusion of all else but an occasional larval or adult insect, etc.)."


_Spawning Season_

Specimens of _H. g. gulonella_ that have been examined reach sexual
maturity at approximately 65 mm standard length. Most specimens of _H.
g. gracilis_ less than 85 mm in standard length are immature, but larger
specimens probably are mature.

The spawning season is in late summer, beginning in July and extending
into September. Specimens from the Peace River, collected on August 10,
1952, include females that were mostly spent and tuberculate males.
Males and females in spawning condition were collected in the Milk River
in August of 1955. A large prespawning female was obtained in Red Deer
River in June of 1952. A male from Fort McMurray had fairly well
developed tubercles on August 9, 1955. A prespawning female was taken
from the Saskatchewan River at Clarkboro Ferry on June 7, 1957.
Tuberculate males were collected in the Powder River on June 30, 1957.
Specimens from the White River in South Dakota, collected on July 7,
1934, include tuberculate males. The specimens discussed above are _H.
g. gracilis_ or intergrades tending toward that subspecies.

Specimens of _H. g. gulonella_ collected in the Arkansas River at Pueblo
and Florence, Colorado, on September 7, 1959, include some tuberculate
males, although most females are spent. On August 8, 1957, a series of
flathead chubs that includes tuberculate males was collected in the
Redwater River, Montana. In the Pecos River on August 25, 1958,
spawning seemingly had been completed, although a few males still bore
tubercles.

TABLE 1. ORGANISMS FOUND IN STOMACHS OF HYBOPSIS GRACILIS FROM VARIOUS
LOCATIONS, EXPRESSED AS PERCENTAGE OF TOTAL VOLUME.

  A: S. Saskatchewan R., Clarkboro Ferry, Sask.
  B: Milk R., Alberta
  C: Missouri R., S. D.
  D: Missouri R., Neb.
  E: Arkansas R., Fremont Co., Colo.
  F: Arkansas R., Pueblo Co., Colo.
  G: Pecos R., San Miguel Co., N. M.

  ==============================+=====+=====+=====+=====+=====+=====+=====
                                |  A  |  B  |  C  |  D  |  E  |  F  |  G
  ------------------------------+-----+-----+-----+-----+-----+-----+-----
  No. specimens examined        |  1  |  7  |  6  | 10  | 10  | 10  | 10
                                |     |     |     |     |     |     |
  No. specimens containing food |  1  |  6  |  1  |  2  |  1  |  3  |  7
  ------------------------------+-----+-----+-----+-----+-----+-----+-----
  KIND OF ORGANISM              |     |     |     |     |     |     |
                                |     |     |     |     |     |     |
  Aphasmidia                    |10.0 |00.7 |     |03.0 |     |     |
  Arthropoda                    |     |     |     |     |     |     |
    Araneae                     |     |     |     |     |     |     |
      Argiopidae                |     |     |     |     |04.0 |     |
      Theridiidae               |     |     |     |     |04.0 |     |
    Insecta                     |     |     |     |     |     |     |
      Ephemeroptera (nymph)     |     |     |     |     |     |     |
        Baetidae                |     |05.0 |     |     |     |     |
        Heptagenidae            |     |08.0 |     |     |     |     |
      Hemiptera                 |     |     |     |     |     |     |
        Corixidae               |35.0 |00.3 |     |     |     |     |
      Hymenoptera               |     |     |     |     |     |     |
        Formicidae              |     |21.0 |     |     |     |     |60.0
      Coleoptera                |     |     |     |     |     |     |
        Staphylinidae           |     |01.7 |07.0 |     |     |     |
        Scolytidae              |     |13.3 |70.0 |     |     |     |
        Tenebrionidae           |     |05.7 |     |     |70.0 |     |
        Carabidae               |     |05.7 |     |     |     |01.0 |
        Curculionidae           |     |01.0 |     |     |     |     |
        Coccinellidae           |     |     |     |     |     |     |09.0
      Trichoptera (case)        |     |01.7 |     |     |     |     |
      Diptera                   |     |     |     |     |     |     |
        Mymaridae               |     |00.3 |     |     |     |     |
        Empididae               |     |01.3 |     |     |     |     |
        Cecidomyiidae           |     |     |     |     |04.0 |     |
        Trachinidae             |     |00.7 |     |     |     |     |
        Simulidae               |     |06.7 |20.0 |     |     |     |
        Tabanidae               |     |     |     |     |06.0 |     |
        Chironomidae            |     |     |     |     |06.0 |     |
        Not identified to family|     |01.0 |     |     |     |     |
      Orthoptera                |     |     |     |     |     |     |
        Locustidae              |     |07.7 |     |     |     |     |
        Tettigoniidae           |     |     |03.0 |70.0 |     |     |09.0
        Tetrigidae              |     |     |     |     |06.0 |     |
      Homoptera                 |     |     |     |     |     |     |
        Fulgoridae              |     |05.0 |     |     |     |     |01.0
      Insect egg                |     |00.7 |     |     |     |     |
  Plants                        |     |     |     |     |     |     |
    Cyanophyceae                |     | 09.0|     |     |     | 99.0| 20.0
    Cyperaceae                  |     | 02.0|     |     |     |     | 01.0
    Zannichellia palustris      |     | 00.3|     |     |     |     |
    Vascular remains            | 55.0|     |     | 27.0|     |     |
                                |     |     |     |     |     |     |
  Miscellaneous                 |     |     |     |     |     |     |
    Sand                        |     | 00.7|     |     |     |     |
    Pharyngeal tooth            |     | 00.3|     |     |     |     |
                                +-----+-----+-----+-----+-----+-----+-----
      Total (%)                 |100.0| 99.8|100.0|100.0|100.0|100.0|100.0
  ------------------------------+-----+-----+-----+-----+-----+-----+-----

Spawning apparently occurs when river levels recede to the seasonal
lows. In late summer, temperatures of these rivers probably are maximal,
their turbidities are reduced, and their sandy bottoms are stable.
Underhill (1959) reports that this species is rare in the Vermillion
River, a northeastern tributary of the Missouri River, except in autumn
when large numbers occur near the mouth of the river. We suspect that
this is associated with spawning.

[Illustration: PLATE 21

Distribution of collections examined.]

[Illustration: PLATE 22

_Hybopsis gracilis gracilis._ Missouri River, Thurston County, northeast
of Macy, Nebraska. Largest specimen 87.5 mm standard length.]

[Illustration: PLATE 23

_Hybopsis gracilis gulonella._ Pecos River, San Miguel County, 3 miles
south of town of Pecos, New Mexico. Largest specimen 91 mm standard
length.]

[Illustration: PLATE 24

FIG. 1. Top: _Hybopsis gracilis gracilis_, 230.0 mm standard length,
one of the largest specimens examined. Missouri River, Carson
County-Walworth County line, 3 miles northeast of Mobridge, South
Dakota, at mouth of Grand River.

Bottom: _Hybopsis gracilis gulonella_, 121.6 mm standard length, the
largest specimen examined of this subspecies. Beaver Creek, Fremont
County, 10 miles northeast of Florence, Colorado, on Highway 115.]

[Illustration: FIG. 2. Regression of head-depth on standard length in
_Hybopsis gracilis gracilis_ from the Saskatchewan River, and in _H. g.
gulonella_ from Beaver Creek, Arkansas River Drainage (KU 4769).]




DISCUSSION


_Hybopsis gracilis_ is highly variable in several morphological
characteristics, including size and shape of head, body, and fins, and
number of scales, vertebrae, and fin-rays. The variations are correlated
in a way that indicates the existence of two subspecies. One of these,
_H. g. gracilis_, attains large size, and has 1) a slender, streamlined
body, 2) a depressed head that is acutely wedge-shaped in profile, 3)
strongly falcate fins with the dorsal and pelvic fins originating
anteriorly, and 4) many scales, vertebrae, and pectoral fin-rays. The
second subspecies, for which _H. g. gulonella_ is the oldest applicable
name, is small, and has 1) a deep, chubby body, 2) head convex in dorsal
contour (less depressed than in _H. g. gracilis_), 3) fins less falcate
than in the latter subspecies, with the dorsal and pelvic fins
originating more posteriorly, and 4) fewer scales, vertebrae, and
pectoral fin-rays than _H. g. gracilis_. These differences are
consistently expressed throughout the size-ranges of the subspecies, and
in series collected at the same or nearby localities in several
different years. Considerable variability was found in features other
than those mentioned above, but individual variation among specimens
from the same locality and adjacent localities is so great that none is
diagnostic of subspecies. For example, orbital size and length of fins
(but not their falcate shape) are variables that have little diagnostic
value, although both features seem to vary in clinal fashion, with the
higher values in the north.

Variation in _H. gracilis_, as shown in the graphic analysis (Figs. 1
and 2) and distribution map (Plate 21), presents two clines: a
north-south cline and a large-river to small-river (mainly east-west)
cline. The absence of _H. gracilis_ from certain portions of river
systems is a matter of concern. The species has not been found in the
lower Arkansas River and the Rio Grande, nor in sandy tributary creeks
in eastern Kansas and Missouri that appear to provide suitable habitat.
It has already been noted that _H. g. gulonella_ seems to be the
ecological equivalent of _Semotilus atromaculatus_ in streams in which
_S. atromaculatus_ is not found. _S. atromaculatus_ occurs in creeks of
eastern Kansas and Missouri, and may provide interspecific competition
that prevents establishment of the flathead chub in these creeks.
Regardless of cause, the gaps in distribution of _H. gracilis_ tend to
limit gene flow.

Many characters used in the separation of the two subspecies are known
to be influenced by environmental conditions, especially temperature.
Hubbs (1922, 1926, 1941), Schultz (1927), Vladykov (1934), Tåning (1952)
and Weisel (1955), among others, have pointed out a correlation between
temperature (or developmental rate of fish) and the number of vertebrae,
scales, and fin-rays. Likewise, Martin (1949) and Hart (1952) have shown
that the proportions of some body-parts vary in response to temperature
during early development. In _H. gracilis_, the general nature of the
clines found in a majority of characters (but not all characters)
suggests a temperature influence. However, temperature-dependent
variability that has so far been demonstrated experimentally in fishes
is generally of lesser magnitude than the differences distinguishing _H.
g. gracilis_ and _H. g. gulonella_. To our knowledge, the most extreme
differences that have been induced by modification of temperature are
those reported for _Salmo trutta_ by Tåning (1952:181-182), who states:
"Shock treatment produced by especially great changes in temperature
(_c._ 10-14° C), especially during the super-sensitive period [of
somatic differentiation that fixes vertebral number] may produce ... a
difference of 3-4 vertebrae ... in offspring of the same parents." The
difference cited approximates that which distinguishes natural
populations of _H. g. gracilis_ and _H. g. gulonella_. Although we
cannot assume that the sensitivity of the brown trout is the same as
that of the flathead chub, the causative conditions in Tåning's study
could scarcely be expected in nature; furthermore, it seems significant
that extremely high (as well as extremely low) mean numbers of scales
and vertebrae were found at southern localities, and that low mean
numbers of scales and vertebrae were found as far north as Wyoming and
Montana. We think it likely that temperature does influence the
expression of characters in _H. gracilis_, directly in individual
development, and indirectly as a selective mechanism in the evolutionary
process. The extent to which each kind of influence exists can be proved
only by experimental work with both subspecies, which we hope to
undertake at a later date.

Other environmental factors that may have selective influence in this
species are rate of current, volume of flow, and turbidity. Interaction
of these environmental factors could result in genetic fixation of
morphological characters through natural selection. The characters that
distinguish _H. g. gracilis_ from _H. g. gulonella_ seem adaptive to
life in large rivers and small streams. Evidence that these characters
are under limited, direct environmental influence is found among
populations in the Arkansas River System. Although populations in the
Arkansas River have no continuity with populations of _H. g. gracilis_,
upstream-downstream variations like those found in other river systems
are apparent, but in lesser degree. The direction of variation in the
Arkansas River is the reverse of that in the Platte and other
tributaries of the Missouri River. For example, the populations farthest
upstream (Florence, Pueblo) have slightly higher mean numbers of lateral
line scales than do populations from Kansas, downstream.

A remarkable effect of extreme parasitism in _H. gracilis_ has been
described by Hubbs (1927). Very young chubs that harbored numerous
tapeworms (_Proteocephalus_) had unusually large numbers of lateral-line
scales, large eyes, short snouts, small fins, small mouths lacking
barbels, and coalescent nares (internarial bridge weak or absent). Some
of these abnormalities presumably resulted from retention of larval
characteristics of the fish, correlated with the degree of infestation
by tapeworms. No teratological adults were found, indicating that severe
infections prevent survival to maturity.

_H. g. gracilis_ occurs in three separate river systems (Mackenzie,
Saskatchewan, Missouri-Mississippi) from latitude 36° N to 66° N, and
longitude 89° W to 123° W. _H. g. gulonella_ exists as several
seemingly-isolated populations in the upper parts of the Rio Grande,
Pecos, South Canadian, Cimarron, Arkansas, Platte, and upper Missouri
basins, from latitude 35° N to 48° N, and longitude 97° W to 100° W.

There is evidence of high mobility on the part of both subspecies, based
on irregularity of their occurrence in certain localities. Many
collections have been made in the Cimarron River in the vicinity of
Kenton, Oklahoma, from 1925 to the present, but only one of these (in
1957) contained flathead chubs. Bait dealers who seine the South
Canadian River in Dewey County, Oklahoma, have taken flathead chubs in
abundance in some seasons, but not at all in others. Seasonal variation
in abundance in the lower Vermillion River, South Dakota (Underhill,
1959:100) has been cited, and the number collected in the lower Kansas
River near Lawrence has varied similarly. Many rivers occupied by _H. g.
gulonella_ (and by intergrades) are intermittent, and in some years
their sand-filled channels become wholly dry for many miles. These
factors probably promote mixing of the two subspecies, and may account,
over long periods of time, for the wide dispersal of _H. g. gulonella_
in the Missouri Basin. Flathead chubs are known from Pleistocene beds at
Doby Springs, Oklahoma (the Doby Springs local fauna) (Smith, 1958:177).
Drainage connections between the Arkansas, Kansas and Platte river
systems existed in Kansan and Nebraskan times (Frye and Leonard,
1952:189-190). Populations that have subsequently become isolated in
those rivers could be accounted for in this way. Flathead chubs could
have entered the Rio Grande-Pecos system by stream-capture from the
Arkansas System, in northeastern New Mexico or southern Colorado. _H. g.
gracilis_ undoubtedly entered the Saskatchewan and Mackenzie basins from
the upper Missouri Basin, following glacial retreat (Walters, 1955:347).




LITERATURE CITED


AGASSIZ, L.

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BAILEY, REEVE M.

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  1956. A check-list of the fishes of Iowa, with keys for
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BECKMAN, WILLIAM C.

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BRYANT, FRANCIS T.

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CHURCHILL, EDWARD P., and WILLIAM H. OVER.

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CLEARY, ROBERT E.

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CLEMENS, W. A., A. MACDONALD, H. MCALLISTER, A. MANSFIELD and D. RAWSON.

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COCKERELL, THEODORA D. A.

  1927. Zoology of Colorado. Univ. Colorado, Boulder. 1-262.

COPE, E. D.

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  1879. A contribution to the zoology of Montana. Amer. Nat.,
        13:432-441.

COPE, E. D., and H. C. YARROW.

  1875. Report upon the collections of fishes made in portions of
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        during the years 1871, 1872, 1873, and 1874. _In_ Report upon
        geographical and geological explorations and surveys, west of
        the one hundredth meridian, in charge of First Lieut. Geo. M.
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CRAGIN, F. W.

  1885. Preliminary list of Kansas fishes. Bull. Washburn Lab. Nat.
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_Transmitted November 8, 1960._


28-5871


[Transcriber's Note:

The following changes have been made to the original text:

    Table of Contents: page number of "Food" and "Spawning Season"
                      changed from 339 to 338
    Page 327: "abbreviated AU" changed to "abbreviated UA"
    Page 344: "Societe Geologique" changed to "Société Géologique"]