68 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY— II. 



ingly large, forming nearly half the length of the side of the head in 

 the smaller specimen, and about two-fifths in the larger. 



The type of R. selenops is No. 19844 in the United States National 

 Museum, from Chattanooga, Tenn. ; length 8 inches. Another is from 

 Montgomery, Ala. ; and I have seen still others from the Cumberland 

 Eiver. 



The following analysis of the species of Hyodon is drawn up from nu- 

 merous specimens of H. chrysopsis taken by Dr. Elliott Cones, natural- 

 ist of the northern boundary survey, in Quaking Ash Eiver; from speci- 

 mens of H. tergisus from Ohio, and from the types of H. selenops. It 

 will be noticed that the characters of H. tergisus are exactly intermedi- 

 ate, corresponding with the geographical range of the species. H. 

 chrysopsia and H. selenops are, therefore, geographical races or varieties 

 which have become so strongly differentiated from the common type 

 that we are able to characterize them as species : 



*> Dorsal fin reduced, and with only about nine fully developed rays ; abdomen sharply 

 carinated (Elaifonistius) : 

 i. Dorsal fin very small, of about nine developed rays (besides the two or three rudi- 

 ments), the length of its longest rays half greater than the length of the base of 

 the fin ; body deep, closely compressed ; the belly strongly carinated both before 

 and behind ventrals ; eye moderate (about 3^ in head); scales rather closely imbri- 

 cated, 5-58-8; i>ectoral fins falcate nearly as long as the head, nearly or quite 

 reaching ventrals; anal with 30 or 31 developed rays ; head 4^ in length ; depth 



3j Chrysopsis. 



•'. Dorsal fin moderate and with eleven or twelve fully developed rays; abdomen 

 more or less obtuse {Hyodon) : 

 1, Dorsal fin larger, of about 12 developed rays ; its longest rays scarcely longer than 

 the base of the fin ; form of body intermediate ; the belly in front of ventrals ob- 

 tusely carinated ; eye large, about 3 in head ; scales medium, 5-58-8 ; pectoral fins 

 decidedly shorter than head, not reaching nearly to ventrals ; anal rays 28 or 29 ; 



head 4J in length, the depth about 3 Tergisus. 



tt Dorsal fin moderate, of 11 or 12 developed rays, nearly as long as high in front; 

 body elongate, not greatly compressed ; the belly in front of ventrals transversely 

 rounded, not carinated ; eye very large, about 2^ in head ; scales loosly imbricated, 

 4-.50-7 ; pectoral fins considerably shorter than head, not reaching nearly to ven- 

 trals ;• an ui rays 27 ; head 4^ in length ; depth about 4 Selknops. 



