Jordafi and Ever mann. — Fishes of Korih America. 255 



with small tubercles. A very large group of small fishes, especially 

 characteristic of the fresh waters of the Eastern United States. 



As here understood, Xotrojns contains about 100 species of small Cvpri- 

 noids. all of them confined to the streams of North America east of the 

 Rocky Mountains. They are in some respects a degenerate type — proba- 

 bly of comparatirely recent origin and perhaps descended from such forms 

 as the European Jlburnus and Leuci-<cus. They are feeble fishes of small 

 size, none of them of value as food for man, but of great importance as 

 food for the larger predatory fishes, particularly the Centrarchida. The 

 species are highly variable, readily affected by surrounding conditions 

 while the really distinctive characters are very few. The identification of 

 species is very diflicult and in the case of young specimens often impos- 

 sible. The following analytical key must be used with great caution as 

 all characters are subject to individual variations. Even the dentition is 

 subject to variations, the ancestors of the group having probably origin- 

 ally had grinding surfaces to the teeth, this becoming rudimentary in 

 some forms and disappearing altogether in others closely related. Vari- 

 ous attempts have been made to break up this group into smaller genera, 

 by subdivision according to the dentition. The various groups heretofore 

 proposed by Girard, Cope, and Jordan seem at the most to indicate sec- 

 tions of slight systematic value. The most practicable division is that 

 made in the Synopsis of Fishes of North America, by whicL the name 

 Xotropis (Minnilits) is retained for the species having the teeth 2, 4—4, 2, 

 while those with but one tooth in the inner row, or with the inner row 

 wanting, would stand as Alburnops. The frequent presence of two teeth 

 in one or both inner rows in two species (heterodon, hudsonius) belonging 

 to Alburnops, renders this division of the genus unsatisfactory. (vtJrof, 

 back ; Tp6-ic, keel, but the supposed keel of Rafinesque's type was due to 

 shriveling in drying.) 



a. Teeth 4-4; 1, 4-4, 0; or 1, 4-4, 1, (sometimes two teeth in one or both inner rows in A", hud- 

 sonius and A', heterodon). 

 b. Scales not very closely imbricated, not notably deeper than long: dorsal inserted nearly 

 over the ventrals: anal short, its rays 7 or 8; no black spot on dOrsa! fin. 

 c. Teeth one-rowed, 4-4, the grinding surface more or less developed at least on one 

 or two teeth. (Teeth sometimes 2, 4-4, 2 in X heterodon.) 

 AzTECA, (Aztec, the ancient rulers in Meiirot: 

 d. Scales small, about 50 in lateral line; body compressed; scales before the dorsal 

 smnll; head blunt, nearly round; coloration plain. azteccs, 400. 



dd. Scales moderately large, .31 to 45 in lateral line. 

 Chriope, (xpeia, want; ut-ri, aperture): 

 e. Lateral line usually (but not always) more or less incomplete; scales before 

 the dorsal large. Small species, usually with a dusky lateral band. 

 /. Snout very obtuse; lower jaw not projecting. 



g. Mouth moderate, the maxillary extending to opposite front of eye 



or nearly so. 



h. Chin black. BirBES.\Trs, 401. 



hh. Chin pale. jordaxi, 402. 



gg. Month very small, the maxillary not nearly reaching front of eye. 



i. Chin pale. mactlatts, 4(B. 



u. Chin black. AXOGExrs, 404. 



^. Snout rather pointed; lower jaw projecting. 



j. Mouth very small: chin pale. caitga, 4(6. 



JJ. Mouth moderate; chin black. uetebodon, 406. 



