134 Field Museum of Natural History — Zoology, Vol. X. 



4 species being common to both sides. Two of these occur on the 

 divide in upland streams, one from the lowlands to the highest altitude 

 attained in Costa Rica by any fish, while the remaining one is taken in 

 the brackish and salt water near or on the coasts. All except two of the 

 PceciliidcB are viviparous. The one, Haplocheilus dovii, nearest to Fundu- 

 lus, has been taken only in salt and brackish water on the Pacific side 

 of Costa Rica, the other Rivulus isthmensis occurs in small upland 

 streams. The remaining fishes taken in the fresh waters of Costa 

 Rica belong to families, most of whose members live in salt water. 

 Some of these have become established in fresh water and are properly 

 fresh-water fishes; the others are really salt-water fishes which have 

 been taken occasionally in fresh waters. 



The fish fauna of Costa Rica is mostly like that of the Nicaragua 

 Lake region. This relationship will be more marked when the lowland 

 streams of both Nicaragua and Costa Rica will have been more thor- 

 oughly explored. 



While the fish fauna of Costa Rica is essentially that of South Amer- 

 ica, it is not likely that its fishes migrated from South America along 

 Panama within recent geological times. Whatever its ancestors may 

 have been, or what may have been their relation with those of South 

 America, we must regard Central America as a somewhat remote center 

 of distribution. From recent studies by Mr. Hildebrand and myself 

 in the region of the Canal Zone, it is quite evident that strictly South 

 American migrants in comparatively recent times did not go far beyond 

 the Canal Zone and that most of these are lowland forms which came 

 from the streams on the Atlantic side of Colombia to the Pacific side 

 after the last gap (Atrato-Tu3rra) here between the two oceans was 

 closed. We find Curimatus, Ctenolucius and G aster opelecus and 

 other Colombian Atlantic forms in streams opposite the Rio 

 Chagres, but not in it. Some Loricarids occur in these streams and 

 also in the Rio Chagres, but these appear to us to have probably crossed 

 from the Pacific side streams to the Chagres and not to have migrated 

 from the rivers of Colombia to the Chagres direct. The distribution 

 of the fresh-water fishes of central Panama will be treated of in detail 

 by Meek and Hildebrand in their report on the fishes of the Biological 

 Survey of the Canal Zone. 



