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 H. 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 
River. 
The following analysis of the species of Hyodon is drawn up from un- 
merous specimens of H. chrysopsis taken by Dr. Elliott Coues, natural- 
ist of the northern boundary survey, in Quaking Ash River; 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. 
chrysopsis 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 (Elattonistius) : 
t. 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 34 in head); scales rather closely imbri- 
cated, 5-58-8; pectoral fins faleate nearly as long as the head, nearly or quite 
reaching ventrals; anal with 30 or 31 developed rays; head 44 in length; depth 
Deb fafe Mbiatala bine SEL See Shed ee Saleen eels Stacie a eee s Sioeta Moe orca eae CHRYSOPSIS. 
**,_ Dorsal fin moderate and with eleven or twelve fully developed rays; abdomen 
more or less obtuse (Hyodon) : 
t. 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'4;indeneth, the depthiabout 3-2 -s.2.2-2oee eects eee ee eee 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 24 in head; scales loosly imbricated, 
4-50-7 ; pectoral fins considerably shorter than head, not reaching nearly to ven- 
trals; anal rays 27; head 44 in length; depth about 4 ..... eS isteteioee SELENOPS. 
