146 THE CYPRINODONTS. 
on the pharyngeals they form a card, and have a slight shoulder, as in 
Rivulus. 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 dpeorids, 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 ; Pace 
seales granulate ; 
mouth large; teeth many Cuvieri 147 
mouth small; teeth few Pentlandii 148 
scales striate ; mouth small elegans 149 
Medium ; 
scales striate; crown flat; mouth large Milleri 149 
scales smooth, in part; crown convex; mouth small Agassizii 150 
Short; belly naked; 
body rounded; head rounded ; 
mouth small; scales striate olivaceus 152 
