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.