male with anal origin nearer snout tip than end of depressed 
organ; about midway in larger examples; organ 2 to a in 
body to caudal base. 
Color in alcohol: brownish, lower surface uniformly 
pale. Edges of each scale dark, forming reticulating pattern. 
Vertical dusky blotch below last dorsal rays. About 12 nar- 
row dark brown streaks vertically in male, more wide-spread 
on caudal peduncle, and dark spot at caudal base. 
Length 20 to 38 mm. We also include besides one in the 
Wilkes Collection from Rio Janeiro, 2 females in the Acad- 
emy from Rio Grande do Sul and a male and female from Puerto 
Bertoni, Paraguay. 
Poecilia vivipara Schneider, 
Head 3 to 3 2/3; depth 3; D. i, 3; scales 24 
to 27 in median lateral series to caudal base ae 8 SOF 
more on latter; 9 scales transversely at dorsal and ventral 
origins; 13 predorsal scales to head; snout 3; to 3 2/5 in 
head; eye 3 1/5 to 3¢ ; mouth width 2 2/5 to 2 2/3; inter- 
orbital 1 7/8 to 2. Body compressed, female deeper bodied. 
Head width 1} to 1 2/5 its length. Snout brosd, depressed, 
length 2: in width. Hind eye edge sabout midway in head, 
Teeth fine, slender, ends spatulate, in outer row; finer 
parallel minute teeth in inner row. Interorbital flat. 
Gill-rekers about 2e short flexible points on ceratobranch- 
ial, about 1/8 of g amen Scales with 13 to 16 besal 
