140 THE CYPRINODONTS. 
Rivulus isthmensis sp. n. 
D) 9-Al V1 Wi 637 Pe Vos 2 e elitr-as: 
Elongate, compressed posteriorly, depressed forward. Head broad, much 
depressed, flattened on the crown, three tenths of the length without the 
caudal. Snout medium, blunt, half as long as the eye. Eye one third of the 
head, twice the snout, less than the interorbital space. First ray of the dor- 
sal over the middle of the base of the anal, two thirds of the distance from 
the head to the base of the caudal. First ray of anal midway from head to 
caudal, last ray nearly as far back as that of the dorsal. Caudal elongate, 
pointed, as long as the head. 
Light olivaceous, with a dark blotch at the base of the dorsal and an- 
other on the back above or in front of the first ray of the anal. Apparently 
there is a light transverse streak at the base of the caudal. 
Rio San José, Costa Rica. 
Rivulus obscurus sp. 2. 
D6; A. 8; V. 65 Be 12/5 .Gl 20) hte s: 
Moderately slender, shaped like FR. cylindraceus. Head broad, flat on the 
crown, much wider than deep, three elevenths of the length to the caudal. 
Snout broad, blunt, rounded, little more than half as long as the eye. Mouth 
wide, lower jaw longer, upper short. Eye large, one third of the head, 
twice the snout, two thirds of the interorbital space. Origin of dorsal 
behind the base of the anal, three fourths of the distance from the middle 
of the eye to the base of the caudal. Origin of anal half way from head to 
caudal; about one half of the base is in front of that of dorsal. Ventrals 
small, hardly reaching the anal. Caudal long, pointed, longer than the 
head. 
Light brownish on the back; with or without brownish blotches, among 
which, on each side of the vertebral line, there 1s a series of three or more 
light blotches. Snout whitish on the top; occiput dark. 
Lake Hyanuary. 
Rivulus atratus sp. n. 
Bo; D.65 AS91105 VG Paley Siesta: 
Elongate, rather slender, depressed forward, compressed behind the vent 
somewhat less than in any of the other species, depth about one sixth of the 
