112 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



process of leasoniug uot uow expiaiuable, Professor Agassiz ideatified 

 this with tbe coinmou Cbub Sucker of the West, a species wliich I con- 

 sider ideutical with Cyprinus oblongus Mitchill. He thus transferred the 

 name Moxostoma from the '• Ked Horse" to the ''Chub Sucker" group. 

 Rafiuesque's description, however, renders it evident that his fish was 

 one of the Red Horse kind; and as Moxostoma is the first generic name 

 applied to species of that group, it must be retained in spite of the 

 incompleteness of the original diagnosis. 



Teretulus Rafiuesque was proposed three pages later for "an extensive 

 subgenUwS, to which belong all the following species of Le Sueur : C. au- 

 reolus, C. 7uacrolepidotus, C. lougirontrum, C. nigricans, C. v'ttatus^ G. 

 macnlosus, C. sticetta, besides the fJ. teres and C. oblongus of IMitchill." 

 To these he adds his own species, G. melanops, G. melanotus (= Gampo- 

 stoma), G.fasciolar is, G. erythrnrus, -dud C. flexuosus. This ^'- omnium ga- 

 tlierum'''' receives the following diagnosis: — "Body elongate cylindrical 

 or somewhat quadrangular, 9 abdominal rays, dorsal fin commonly smoll, 

 tail equally forked." 



A name proposed for a group of tins kind, in the opinion of the pres- 

 ent writer, should not be set aside, but should be retained for some one 

 oi more of the species originally referred to it, and when any writer 

 adopts such a genus, he shall have the right to select any of the species 

 as its type, and the name should be considered thereafter as applying 

 to such typical species only, not to be revived in case such typical species 

 be afterwards found to have had a prior generic name. In case no such 

 type has been selected by any author, then the "principle of exclusion" 

 should be applied, and the name be retained for such species as may be 

 left to the last, on subtracting from tbe mongrel group the different 

 component genera in chronological order. 



In this view, Teretulus, having been by Professor Cope, in 18G8, re- 

 stricted to G. aureolus Le S. and its affines, these being congeneric with 

 species previously called Moxostoma, becomes a synonym of Moxostoma, 

 and cannot be used for a distinct genus. The principle of exclusion, 

 if unmodified, would require us to use the name Teretulus for those 

 species left on subtracting Gatostonius proper, Moxostoma^ Gampostoma, 

 Erimyzon, and Hypentelium, i. e., in place of Minytrema. 



Ptychosfomus Agassiz was i)r()posed for this same group, without 

 reference to the two names conferred by Rafinesque, This genus was 

 well characterized by Professor Agassiz on the peculiarities of the scales 



