328 Fretp Museum or Natura History — Zoétoey, Vor. X. 
the basal half of the dorsal and caudal fins black, the distal half of the 
latter often yellow, a condition not conspicuous on west coast specimens. 
The fresh water individuals are much more uniform in color, and 
usually smaller than those from salt and brackish water. Those taken 
from fresh water might be regarded as a variety under the name Mol- 
lientsia sphenops gillit (Kner & Steindachner). 
This species is represented by numerous specimens in the present 
collection. The largest females are roo and the largest males 78 mm. 
in length. It occurs abundantly in quiet ponds and arms of the rivers 
and creeks of both slopes of Panama, but not in the Rio Tuyra Basin. 
The males of this species are so large that they are pretty certainly 
caught along with the females and do not escape through the meshes of 
the net, as has been stated of other viviparous species of this family, 
in explanation of the small number of male specimens occurring in col- 
lections. For this reason we have counted 2,142 specimens collected 
at various points and on various dates during two periods of the two 
years during which these collections were made. Among this number 
there are 579 males or nearly 3.7 females to every male. The disparity 
of males to females is, however, believed, in reality, to be greater than 
these figures indicate, for this species was many times taken in such 
abundance that only a small number of them was preserved. In such 
FiG. 10. DISTAL PART OF INTROMITTENT ORGAN OF Mollicnisia sphenops 
(Cuvier & Valenciennes). (Greatly magnified.) 
cases, due to the fact that the males are more brightly colored and thus 
more conspicuous, it is quite probable that more than their proportion- 
ate number was selected, although we do not remember that any par- 
ticular attention was given to this matter at the time. 
Habitat: Coasts and rivers from Sinaloa, Mexico, both slopes of 
Panama, south to eastern Colombia, Venezuela and the Leeward 
Islands. 
