_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).

Geographic Variation in the North American Cyprinid Fish, Hybopsis gracilis — Part 5

_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.).

Geographic Variation in the North American Cyprinid Fish, Hybopsis gracilis — Part 5

_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).

Geographic Variation in the North American Cyprinid Fish, Hybopsis gracilis — Part 5

_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.