46. SALMONID^ MICROSTOMA. 289 



dd. Scales larger, similar in both sexes; pectoral rays 10-12. 



e. Teeth feeble, those on tongue very weak ; scales small, adherent. 



THALEICHTHYS, 141. 



ee. Teeth stronger, those on tongue enlarged ; scales moderate, decid- 

 uous OSMERUS, 112. 



cc. Ventrals inserted under or behind the middle of dorsal; mouth moderate 



or small. 

 f. Scales cycloid. 



g. Jaws with minute teeth ; maxillary reaching past front of eye. 



HYPOMESUS, 14:3. 

 gg. Jaws toothless; maxillary not reaching front of eye. 



ARGENTINA, 144. 



jf. Scales ctenoid HYPHALONEDRUS, 145. 



** Pyloric co?ca many ; stomach siphonal. 



tJaws toothless or with a few feeble asperities; scales rather largo; anal fin 



somewhat elongate; maxillary short and broad ; not u- 



adromous ( Coregoiiiiict}) COKEGONUS, 146. 



tt Ja\vs with distinct teeth; scales mostly small. (Salmonince.') 



1i. Dorsal iiii very long and high, of about 20 rays; scales mod- 

 erate; tongue toothless; not auadromous. 



THYMALLUS, 147. 



hh. Dorsal fin moderate, its rays 9-15 in number; tongue with 



teeth. 



i. Dentition very feeble, incomplete; anal fin elongate, of about 

 17 rays; scales moderate; not auadromous. 



STENODUS, 148. 



ii. Dentition strong and complete; conical teeth on jaws, vo- 

 mer, and palatines ; tongue with two series of strong 

 teeth (deciduous in very old specimens of Oncorhynchus); 

 scales small. 



j. Anal fin elongate, of 14-17 rays; vomer narrow, long, flat, 

 with weak teeth; species black spotted. 



ONCORHYNCHUS, 150. 

 ij. Anal fin short, of 9-11 developed rays. 



k. Vomer flat, its toothed surface plane; teeth on the shaft 

 of the vomer in alternating rows or in one zigzag row, 

 those on the shaft placed directly on the surface of tho 

 bone, not on a free crest (posterior vomerine teeth some- 

 times deciduous) ; species black spotted SALMO, 151. 



Ick. Vomer boat-shaped, the shaft strongly depressed, with- 

 out teeth ; very small, about 200 in the course of the lat- 

 eral line; species not anadromous, spotted with red or 

 gray SALVELINUS, 152. 



13. THICROSTOMA Cuvier. 



(Cuvier, Regne Auim. ii, 1817: type Gasteropelecus microstoma THsso=Microstomaro- 

 tundatum Risso.) 



Body elongate, cylindrical, covered with large, thin, silvery scales. 

 Head short. Mouth very small, terminal; premaxillaries very small; 

 maxillaries very short and broad, not extending to the front of the very 

 large eye, which forms more than half the depth of the side of the head. 

 Lower jaw and vomer with a narrow series of fine teeth; no other teeth. 



Dorsal fin short, inserted before or behind the veutrals, which are behind 

 Bull. Nat. Mus. No. 1C 19 



