134 Fretp Museum or Naturat History— Zodétocy, Vou. 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 
Peciliide 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 tsthmensis 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 Nicasagam 
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-Tuyra) here between the two oceans was 
closed. We find Curimatus, Ctenolucius and Gasteropelecus 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. 
