202 Bulletin ^7, United States National Museum. 



A. Dorsal fin short, without developed spiuo ; no anal spine. 

 Campostomin.k : 

 a. Air bladder surrounded by many convolutions of tlio very long alimentary canal ; herbiv- 

 orous. 

 6. Teeth 4-4, or 1, 4-4, 0, with oblique grinding surface and slight hook ; peritoneum 

 black. Campostoma, 100. 



an. Air bladder above the alimentary canal, as usual in fishes. 



ClIONl)R()STOMIN,»;.* 



c. Intestinal canal elongate, usually more than twice the length of the liody ; teetli 1-rowed, 

 with grinding surface well developed; peritoneum iisually black; herbivorous. 

 il. Teeth 6-6, strongly compressed, knife-shaped ; pseudobranchia; none ; rudimentary 

 caudal rays greatly developed; scales very small. Orthodon, 101. 



dd. Teeth S-T) or 4-5 ; dorsal fin inserted posteriorly ; scales small. 



e. Pseudobranchia; none ; lower jaw thin, with hard, sharp edge ; upper jaw pro- 

 tractile, with fleshy covering; body elongate, subterete. Ox voeneum, lOi. 

 ee. Pseudobranchia? present. 



/. Jaws each with a conspicuous, broad, straight-edged, horny plate ; teeth 

 4-5, stout, bluntish, hooked, and short. Acrocheii.us, 103. 



ff. Jaws without horny plate. 



g. Lateral line complete ; rudimentary caudal rays numerous ; anal basis 

 elongate. Lavinia, 104. 



gg. Lateral line incomplete ; anal basis short ; scales minute. 



CllROSOMUS, 105. 

 d&A. Teeth 4-4 ; dorsal fin nearly median ; jaws without horny plate. 



h. First (rudimentary) ray of dorsal slender, firmly attached to the first developed 

 ray, as usual among fishes. 

 i. Scales very small, 55 to 72 in the lateral line, which is complete. 



Aloansea, 106. 

 ii. Scales larger, 35 to 45 in the lateral line. Hybognathus, 107. 



hh. First (rudimentary) ray of dorsal somewhat enlarged and blunt, connected by 

 membrane with the first developed ray. 



PiMEPHALES, 108. 



tc. Intestinal canal short, less than twice the length of the body ; peritoneum usually 

 pale ; teeth 1 or 2-rowed ; carnivorous or partly so. 



MTLOPHARODONTINiE : 



j. Teeth scarcely hooked, some or all of them molar, blunt, or stump-shaped, much 

 enlarged and obtusely truncate ; large, coarse fishes. 

 A-. Teeth 2, 4-5 or 5-5, 2. 



I. Upper jaw not protractile; no baibels. Mylophabodon, 109. 



//. Upper jaw protractile ; maxillary with a barbel. Mylocheilus, 110. 



)ck. Teeth 3-3; upper jaw protractile. SrvronoN, 111. 



j;. Teeth hooked, slender, none of them molar, the grinding surface, if present, nar- 

 row or rudimentary. 

 Letjciscin^ : 

 ni. Lower jaw normally formed, the dentary bones curved, free from each other, 

 except at the symphysis. 

 n. Teeth in the main row, 5-5 or 4-5. 



o. Abdomen behind ventral fins transversely rounded, the scales passing 

 over it ; the edge not forming a scaleless ridge ; anal base gener- 

 ally, but not always, short. 

 J). Maxillary with a barbel ; premaxillaries protractile. 



q. Barbel minute, not quite terminal ; teeth without grinding 

 surface ; caudal fin symmetrical, its rudimentary basal 

 rays not greatly developed. Semotilus, 112. 



*This subfamily, as here recognized, is extremely heterogeneous. Some of the American 

 genera of herbivorous minnows and chubs, as Orthodon, Acrocheilus. and perhaps Oxiigeveum and 

 Laviuia, are allied to the European (Viotidmsloma. The others may be descended from Leuciscine 

 types, or they may have degenerated from other herbivorous forms. 



