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.