38 VERTEBRATE ANIMALS OF THE UNITED STATES 



bo Gill-rakers short, with 12 to 16 on lower Hmb 2. Prosopinm. 



3. IriUion. 

 32 Lower jaw usually longer than the upper; premaxillaries with the 



cutting edge horizontal or directed forwards 4. Leacichthys. 



I. Coregonus L. Whitelish. Body elongate, compressed; head 

 small; mouth small; teeth minute or wanting; pseudobranchiae large; 

 air bladder very large: 18 species, in clear lakes in the northern hemi- 

 sphere, those in Arctic America descending to the sea; i species in the 

 United States. 



C. clupeaformis (Mitchill) (Fig. 18). Common whitefish. Length 

 600 mm. or more; greatest weight about 23 lbs.; head 4.5 to 5; depth 7,.^ 



Fig. 18. — Coregonus clupeaformis {from Jordan dr' Evermann) . 



to 4; color olivaceous above; sides white; rays of dorsal iin 11; anal 11; 

 scales 72 to 86, usually over 75; branchiostegals 9 to 10; gill-rakers 

 long and slender: Great Lakes and neighboring waters, and north- 

 ward to the Arctic Ocean; abundant; the most valuable food fish in the 

 Great Lakes. The whitefish feeds on small crustaceans and mollusks 

 and lives most of the year in deep water, but in the fall and early winter, 

 at spawning time, it approaches the shores. 



2. Prosopium Milner. River whitefish. Body slender; head short 

 gill-rakers short and thick, 12 to 16 on the lower limb; no teeth on the 

 jaws: 10 species; in northern America; 6 in the United States. 



Key to the United States Species 



ai Species in the eastern and central States. 



bi Upper jaw reaching beyond the front margin of eye P. stanleyi. 



bo Upper jaw not reaching the eye P. quadrilateraUs. 



ao Species in the far west P. ivilliamsoni. 



P. coulteri. 

 P. spilonotus. 

 P. abvssicola. 



