134 THE CYPRINODONTS. 



RIVULUS. 



Rioulus Poey, 1861, Mem., II, 307, 383,-1868. Repert., H, 209, 412 ; Gthr., 1866, Cat, VI, 8'27. 



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. Gill 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, 383,-1868, Pepert., II, 412,-1876, An. Soc. Esp., 

 V, 140, pi. V, fig. 4,-1880, An. Soc. Esp., IX, 247, pi. VIII, fig. 1; Gthr., 1866, Cat., VI, 327; Jor., 

 1887, P. U. S. Mus., IX, 564. 



Rivulus marmoratus Poey, 1880, Au. Soc. Esp., IX; Jor., 1887, P. U S. Mus., IX, 564. 



B. 6 ; D. 10-11 ; A. 13 ; V. 6 ; P. 14 ; LI. 38-39 ; Ltr. 11-12 ; Vert. 



15 + 17. 



In this species the form is moderately elongate, compressed behind the 

 body cavity, depre.ssed 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, 



