110 Fretp Museum or Natura History — Zoéiocy, Vor. X. 
Rivulus isthmensis Garman. 
Rivulus isthmensis Garman, Mem. Mus. Comp. Zodél., 1895, 140 
(Rio San José, Costa Rica) ;— Regan, Biol. Cent. Amer., 1907, 
82;— Regan, Ann. & Mag. Nat. Hist., 1912, 503. 
Rivulus flabellicauda Regan, Ann. & Mag. Nat. Hist., 1907, 64 
(Juan Vifias, Costa Rica) ;— Regan, Biol. Cent. Amer. 1907, 81, 
pl. 4, fig. 6 (Juan Vifias and San José, Costa Rica) ;— Regan, 
Ann. & Mag. -Nat. Hist., 1912, 500 (Costa Rica). 
The fact that I had collected so many specimens of this species near 
San José, and found none to agree with the description of Rivulus 
isthmensis, led me to suspect that but one species was found there. I 
sent a few specimens to Mr. Garman and asked him to compare them 
with his types of R. zsthmensis. This he kindly did and informed me 
that they were the same. He states in his letter to me that ‘‘32 (the 
scale count for the lateral line) is in all likelihood an error for 42.” 
San José, April 26 (20), 50 to 70 mm.; San José, April 19 (3), 51 to 60 
mm.; Tucurrique (1), 62 mm. (Alfaro); San José (2), 75 mm. (Alfaro); 
Tobosi (16), 48 to 60 mm. (Alfaro); El Guayabo (3), 54 to 63 mm. 
(Alfaro). 
The following species of Peciliide belong to the subfamily Peciliine, 
which comprises those species in which the anterior rays of the anal 
fin are considerably elongated and modified into an intromittent organ. 
Mr. Regan of the British Museum has recently published (Ann. & Mag. 
Nat. Hist., 1913, 977-1118) a revision of this family, basing his classifica- 
tion chiefly on the modified anal fin of the male. Although my manu- 
script was practically ready for publication when I received Mr. Regan’s 
paper, I have changed it so far as it relates to the species here listed of 
this subfamily to conform to his classification. The males of many of 
the species of Peciliine are so small, and so few in collections, that the 
study of the group is even more difficult than with the old classification. 
It is generally considered that the males of Gam)usia and related 
genera are less numerous than the females, because they are taken in 
comparatively few numbers by collectors. This is, however, practically 
accounted for because of their small size, which enables them to pass 
easily through the mesh of the average collecting net which would 
easily retain the female. 
I give here a key to the genera of this subfamily treated of in this 
paper, which is taken from the one published by Mr. Regan: 
a. Lower edge of caudal peduncle sharp, without a median series of 
