134 THE CYPRINODONTS. 
RIVULUS. 
Rivulus Poey, 1861, Mem., II, 307, 383, — 1868, Repert., I], 209, 412; Gthr., 1866, Cat., VI, 327. 
Body moderately elongate, depressed anteriorly, compressed in the pos- 
terior half. Head depressed, broader than deep, crown flat. Snout short, 
blunt, rounded. Mouth medium; upper jaw shorter, slightly protractile, 
not expanded and produced; symphyses rather firm. Teeth small, sub- 
conical, in bands. Eyes medium to large, lateral. Guill openings wide; mem- 
branes short, partly united, free from the isthmus. Scales thin, flat, striate, 
covering belly and head, except chin to throat. Intestine short. Ventrals 
small. Other fins well developed ; dorsal and anal behind the middle of the 
length, former smaller and farther back; caudal broad, convex to pointed. 
Air bladder present. 
Cuba, Central America, and South America from the La Plata northward. 
The form is more elongate and the dorsal is farther back, compared with 
the anal, than in Fundulus. The structure of the mouth differs much from 
that of Haplochilus, the upper jaw being short and not at all expanded and 
produced forward. The head has not the compressed appearance, nor the 
body the depth, obtaining in Cynolebias. And compared with Pterolebias 
the ventrals are less developed and the caudal section is not so sharp and 
thin. I find the Rivuli to agree with their kindred in the possession of an 
air bladder. 
Rivulus cylindraceus. 
Rivulus cylindraceus Poey, 1861, Mem., II, 308, 883, — 1868, Repert., IT, 412, —1876, An. Soc. Esp., 
V, 140, pl. V, fig. 4, — 1880, An. Soc. Esp., IX, 247, pl. VIII, fig. 1; Gthr., 1866, Cat., VI, 327; Jor., 
1887, P. U. S. Mus., TX, 564. 
Rivulus marmoratus Poey, 1880, An. Soc. Esp., IX; Jor., 1887, P. U S. Mus., IX, 564. 
B.6; D. 10-11; A. 18; V.65 P14; El 38-395 dir 1-2/5, Were, 
Lor 17. 
In this species the form is moderately elongate, compressed behind the 
body cavity, depressed anteriorly, and little, if any, more nearly cylin- 
drical around the middle than some of the other types. Depth about two 
ninths of the total length. Head broad, flattened on the crown, three and 
a half times in the length, without the caudal. Snout broad, blunt, hardly 
as long as the eye. Mouth moderate, superior in aspect, cleft nearly hori- 
zontal; jaws somewhat firmly united. Teeth simple, hooked, firmly set, 
