2 6 UNIVERSITY OF COLORADO STUDIES 



parts white to cream color; sides of the body with a yellowish or greenish cast; 

 mouth and under parts of the head pinkish or yellowish white; ventral parts and 

 the ventral and anal fins more or less orange-red in breeding males; fins hyaline 

 to milky white, upper surfaces of the pectorals and ventrals dusky. Young 

 individuals lighter and more uniformly colored than the adults, the mid-dorsal 

 region distinctly mottled; sides without spots (see C. commersonii sucklii). 



Size large, length up to 2 feet. 



The Gray Sucker occurs in all of our foothill collections in company with 

 Suckley's Sucker. The two species are probably competitors, since the stomach 

 contents show the food to be the same. Two collections made in about the same 

 tjqje of habitat, one in West Plum Creek near Castle Rock and another from 

 Boulder Creek near Boulder, also point to a condition of competition between 

 these two species, since the relative frequency is reversed in the two localities, 

 showing local rather than general dominance of either species. At both stations 

 aU of the fish taken were saved and in both cases the streams were shallow and 

 less than twenty feet wide so that the collections are probably representative. 

 From West Plum Creek 170 Catostotnus commersonii sucklii and 26 Catostomus 

 griseus were taken, a ratio of nearly 7 to i, while from Boulder Creek 120 C. griseus 

 were collected and but 49 C. commersonii sucklii, a ratio of a little less than 3 to i 

 in favor of the Gray Sucker. One of the disturbing factors which probably entered 

 into the West Plum Creek competition was the presence of large numbers of larval 

 trematodes, nearly all of the Gray Suckers and but a few of the Suckley Suckers 

 being infected, this unequal infection with a parasite giving a possible advantage 

 to the Suckley Suckers. Both species are occasionally infected with this larval 

 trematode in Boulder Creek. 



Catostomus griseus is known only from the western portions of the Platte 

 River and its tributaries. 



Colorado specimens. — University Museum: Boulder Creek near Boulder, October, 1903 (102 

 specimens, 30-120 mm.), C. Juday and J. Henderson, No. 3; St. Vrain Creek, Longmont, October 

 17, 1903 (9 specimens, 120-180 mm.), C. Juday and D. W. Spangler, No. 5; West Plum Creek 

 near Castle Rock, June 9, 1912 (26 specimens, SS-I55 mm.), A. G. Vestal and M. M. Ellis, No. 317; 

 Boulder Creek 6 miles east of Boulder, July 25, 1912 (125 specimens, 30-160 mm.), M. M. Ellis, 

 No. 318; Colorado Stale Historical and Natural History Museum: South Platte, Denver, August 

 3, 1900 (205 mm.), W. C. Ferril; State Teachers' College Museum: Cache la Poudre near Greeley, 

 A. E. Beardsley. 



Catostomus latipinnis Baird and Girard 



Flannel-mouthed Sucker 



Catostomus latipinnis Baird and Girard, Proc. Acad. Nat. Sci. Phila., p. 388, 1853 (Rio San 

 Pedro, Gila basin); Jordan, Bull. U.S. Fish Com., Vol. IX, p. 26, 1889 (Grand River, Glenwood 

 Springs; Gunnison and Uncompahgre Rivers at Delta). 



Body elongate, terete in large specimens, slightly compressed in the caudal 

 half; depth 5. 5 to 5 in average specimens, about 4.6 in very large adults, in the 



