_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.