146 THE CYPRINODONTS. 



on the pharyngeals they form a card, and have a shght shoulder, as in 

 Rivulns. The gill membranes are partly united, but free from the isthmus. 

 Normally there are five branchial rays. In cases the length of the intestine 

 about equals the total length of the fish ; from this it varies to nearly twice 

 as long ; the stomach is but little differentiated. On the young generally, 

 and throughout life on a few species, the scales are thin and striate ; later 

 stages of particular types are marked by a thickening and enlargement of 

 the scales on the anterior portion of the body and head, which scales are in 

 some species tubercular or granulated, or in others smooth and polished. 

 A medium size obtains in the fins ; dorsal and anal are behind the middle of 

 the body, opposed, and the latter is unmodified in the male ; there are no 

 traces of ventrals. 



The genus inhabits the freshwaters of the upper Andes of South America, 

 especially Titicaca and similar bodies. In these isolated lakes Orestias and 

 a siluroid, Trichomycterus, are so far as known the only genera. Their food 

 is mostly animal. Whether the vegetation of these waters, abundant — such 

 as it is — is at all fit for a vegetable-eating fish, like the carp, can be deter- 

 mined only by an experiment in fish culture, for which it appears as if 

 a grand opportunity is here provided. Valenciennes, in 1839, named this 

 genus, from the Greek word opeo-rias, a nymph of the mountains, on page 

 118 of the journal L'Institut, where he mentions the lack of ventral fins, 

 and enumerates several of the species with their localities and vernacular 

 designations. 



Young individuals of all the species are much alike, even those which 

 become very distinct in their later stages ; for this reason a synopsis that 

 serves to separate large individuals of the different types is of less value 

 when applied to the small ones. The following includes the species recog- 

 nized in these pages. 



Elongate, in adult ; Page 



scales granulate ; 



mouth large ; teeth many 

 mouth small ; teeth few 

 scales striate ; mouth small 

 Medium ; 



scales striate ; crown flat ; mouth large 

 scales smooth, in part ; crown convex ; mouth small 

 Short ; belly naked ; 



body rounded ; head rounded ; 

 mouth small ; scales striate 



