ETHEOSTOMATID^. 9 



The principal characters separating Ericosma from Alvordius are 

 shown below. 



Alvordius, Grd. 



(Type, A. maculatus GvA.) 



Vertebrse numerous, about 44 iu 

 all ; 22 in front of anus. 



Body and head elongate ; mouth 

 wide, with well-developed teeth on 

 vomer and on palatines. 



Sexes similar ; males never with 

 the fins tuberculate. 



Dorsal spines 12 to 15 ; the two 

 dorsal fins well apart. 



Caudal fin slightly emarginate. 



Ericosma, Jordan. 

 (Type, Alvordius evidea Jor. & Copel.) 



Vertebrae fewer, about 39 in all ; 

 17 in front of anus. 



Body short and compact ; mouth 

 small, with about six minute teeth 

 on vomer and none on palatines. 



Sexes dissimilar; the males bril- 

 liantly colored, with the lower fins 

 tuberculate. 



Dorsal spines 10 or 11 ; the two 

 fins contiguous. 



Caudal fin deeply emarginate. 



6. KHEOCRYPTA, Jordan, gen. nov. 



Allied to Imostoma and Alvordius. Body rather slender and elongate, 

 with a pretty large, rather long, and somewhat narrowed head, resembling 

 that of Boleosoma ; mouth small, horizontal, subinferior, with weak 

 teeth in the jaws, five or six small teeth on the vomer, and none on the 

 palatines ; upper jaw protractile, separated by a distinct furrow from 

 the forehead; two distinct dorsal fins, of which the second is rather 

 smaller than the first and than anal; anal with two distinct spines; 

 ventral region with a series of enlarged plates, as in Alvordius and Per- 

 cina, these caducous, in many specimens replaced by a scaleless strip ; 

 cheeks naked ; opercles with a few scales ; lateral line complete. 



This genus is perhaps nearest Imostoma, with which it agrees in the 

 protractile mouth. It differs from Imostoma and agrees with Alvordius 

 Grd. in the presence of ventral plates. The name Rheocrypla [pzd>, to 

 flow rapidly— x/)y7:roc, concealed, L e., hiding in the rapids) is given in 

 allusion to the peculiar habits of this interesting species. 



7. RHEOCRYPTA COPELANDI, Jordan, sp. nov. 



Head 4| in length ; depth 5i ; eye large, 3^ in head ; scales moderate, 

 strongly ctenoid, 56 iu lateral line; those of the ventral much enlarged, 

 forming serrated plates ; cheeks naked ; opercles with a few scales ; neck 

 and throat naked. Fin-rays :— Dorsal X-XII, 10; anal II, 9. 



