SALMONID^, — XXXIY. 77 



aa. Jaws with distinct teeth ; scales smaller. 

 b. Dorsal very long and high, of about 20 rays ; scales medium ; tongue 



toothless Thymalhis, 81. 



bb. Dorsal moderate, its rays- 9 to 15; tongue with teeth; teeth strong; A. 

 short, of 9 to 11 developed rays. 

 c. Vomer flat, its toothed surface plane, the teeth on its shaft in one or 

 two rows, sometimes deciduous ; species black-spotted, with con- 

 spicuous scales Salmo, 82. 



cc. Vomer boat-shaped, the shaft strongly depressed, without teeth ; 

 scales very small, more or less imbedded; species with red or gray 



spots SALVELI^'US, 83. 



80. CORBG-ONtrS (Artedi) Linnaeus. White-fishes. 



(This genus contains about forty species, lake-fishes of northern 

 regions, usually spawning in shallow waters or in brooks in late 

 fall or winter. All are excellent food-fishes, and all are very variar 

 ble.) (The old name, of uncertain origin.) 



a. Lower jaw included ; premaxillaries broad, placed more or less vertically, 

 or the lower edge turned inward ; the cleft of the mouth less than one- 

 third the head. 

 b. Gill rakers short, thickish, about X -|- 16; preorbital broad, wider than 

 pupil ; maxillary short, broad, not reaching to eye ; the supplemental 

 bone narrowly elliptical; supraorbital broad ; mouth very small. 

 (Prosopium Milner.) 



182. C. quadrilateralis Richardson. Round-fish. Pilot- 

 fish. Shad-waiter. Menomonee White-fish. Body sub- 

 terete, the back broad ; maxillary 5^ in head ; head long, the snout 

 compressed and bluntly pointed ; preorbital wider than pupil. 

 Dark bluish, sides paler. Head 5 ; depth 4|. D. 11. A. 10. 

 Scales 9-85-8. N. H. to L. Superior, Alaska, and N. Through- 

 out the Rocky Mountains is found a closely related species, C. wil- 

 liamsoni Girard, with shorter snout and longer maxillary. (Lat., 

 4-sided). 



bb. Gill rakers numerous, long and slender, X -|- 20 to 25 ; preorbital long 

 and narrow; maxillary rather long, the supplemental bone ovate. 

 {Coregonus.) 

 c. Tongue toothless; body robust, elevated at the shoulders in the adult; 

 the head very small, especially in old examples. 



183. C. clupeiformis (Mitchill). Common White-fish. 

 Snout bluntish, obliquely truncate ; preorbital not half pupil ; max- 

 illary past front of orbit, 4 in head ; eye largo ; gill rakers ^ eye. 

 Color pale, scarcely silvery. Head 5 to 6; depth 2\ to 4. D. 11. 

 A. 11. Scales 8-74-9. L. 30. Great Lakes and N. ; by far the 

 most valuable of the American white fishes. Very variable ; feeds 

 on minute organisms. (Clupea, herring ; forma, shape.) 



cc. Tongue with about 3 series of small teeth ; body rather elongate ; the 

 back scarcely elevated. 



