no Field Museum of Natural History — Zoology, Vol. X. 

 Rivulus isthmensis Garman. 



Rivulus isthmensis Garman, Mem. Mus. Comp. Zool., 1895, 14° 

 (Rio San Jose, Costa Rica); — Regan, Biol. Cent. Amer., 1907, 

 82; — Regan, Ann. & Mag. Nat. Hist., 191 2, 503. 



Rivulus flahellicauda Regan, Ann. & Mag. Nat. Hist., 1907, 64 

 (Juan Vinas, Costa Rica); — Regan, Biol. Cent. Amer. 1907, 81, 

 pi. 4, fig. 6 (Juan Vinas and San Jose, Costa Rica); — Regan, 

 Ann. & Mag. Nat. Hist., 191 2, 500 (Costa Rica). 



The fact that I had collected so many specimens of this species near 

 San Jos^, 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. isthmensis. 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 Jos^, April 26 (20), 50 to 70 mm.; San Jose, April 19 (3), 51 to 60 

 mm.; Tucurrique (i), 62 mm. (Alfaro); San Jose (2), 75 mm. (Alfaro); 

 Tobosi (16), 48 to 60 mm. (Alfaro); El Guayabo (3), 54 to 63 mm. 

 (Alfaro). 



The following species of PceciliidoB belong to the subfamily PceciliincB, 

 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, 977-1 1 18) 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 PceciliincB 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'msia 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 



