JORDAN ON FISHES OF DAKOTA AND MONTANA. 785 



generic character, as it is subject to many variations. I find, ho wever, that 

 in those species which have two teeth in the smaller row, that character is 

 very constant. 1 find also that in those genera [Luxilus, Alburnops, Cera- 

 tichthys, Cliola, etc.) in which some of the species possess two teeth in the 

 outer row, while others have no teeth or but one, those species with two 

 teeth are strikingly different in general external characters and appear- 

 ance from the others, and have in each of the above cases been already 

 distinguished as subgenera {Photogenis, Hydrophlox, Upisema), and in 

 all but one have received distinctive names. The Cyprinidw are small 

 fishes, of low organization, and the very numerous species are very 

 closely related. It seems advisable to divide the various forms related 

 to Leuciscus into groups with distinctive names, which we may call 

 " genera", although they may not be exactly co-ordinate with the gen- 

 era of some family less rich in species. To combine them all into one^ 

 genus, as has been attempted by Giinther and Valenciennes, has led 

 only to confusion and the almost utter loss of all knowledge of the spe- 

 cies. Our tests of a " generic character" in such a group must be, Does 

 it hold ? Is it capable of exact definition and determination ? Does it set 

 off species really related, from others of more remote afiQnities ■? At 

 present, the character of the two inner teeth seems to fill these require- 

 ments, and it is therefore held provisionally as a true generic character. 

 It may be premised that this character requires verification in several 

 species now referred to N^otropis, Luxilus, Cliola, Ehinichthys, etc. 



COUESIUS, gen. nov. 



Type. — Leucosomus dissimilis Grd. = Nocomis milneri Jordan. 



Characters. — Leuciscince, with the fins normal, the dorsal over or slightly posterior 

 to veutrals, the basis of the anal short ; mouth normal ; end of the maxillary bone 

 with a small but conspicuous barbel ; scales rather small ; lateral line present ; in- 

 testinal canal short; teeth 2, 4-4, 2, those of the longer row hooked, sharp-edged, with- 

 out grinding surface ; upper jaw protractile. 



This genus is dedicated to Elliott Coues, one of the very foremost of 

 American students of vertebrates, to whose activity as a collector we 

 owe the interesting collection which is the subject of the present paper. 



The following analysis of the genera of American Cyprinidw which 

 now seem to me worthy of recognition will show the relations of the 

 genus Couesius to its afiQnes. 



*, Dorsal fin without a strong, developed spine; ventral fins not decurrent on the 



abdomen, 

 t. Pharyngeal teeth developed. 

 i. Dentary bones straight and flat, united throughout their length ; mandible much 



incurved, tongue-like, a lobe on each side of it 

 at base; air-bladder normal. (Exoglossince.) 

 a. Teeth hooked, 1, 4-4, 1, without grinding surface ; dorsal fin nearly oj)posite 



ventrals ; anal basis short ; no barbel ; premax- 

 illaries not projectile; intestinal canal short. 



EXOGLOSSUM. 



