Dec. 28, 1916. Fisnes or PANAMA— MEEK AND HILDEBRAND. 233 
The two representatives of the family Gobiide taken here by us are 
widely distributed on the Pacific slope of tropical America. 
GENERAL CONCLUSIONS WITH RESPECT TO DISTRIBUTION. 
We regard Panama as a very remote center of distribution and 
believe that the fresh water fishes have mostly migrated to this region 
within comparatively recent geologic times. 
The fish fauna of Panama is essentially that of South America, and 
most of the forms seem to have entered from that direction. The 
families Loricariide, Pygiditde, Cyclopide, Callichthyida, as well as several 
of the representatives of the families Siluride, Characide, Gymnotide 
and Cichlide known from South America reach their northern limit of 
distribution in Panama. The extreme likeness of the fauna of the 
Pacific slope of Panama and that of the Atlantic slope of Colombia, 
and in particular the close similarity of the fishes of the Rio Tuyra and 
the Rio Atrato strongly indicate that the last gap between these two 
streams was closed within comparatively recent times. As i 
stated the watershed between the upper tributaries of these streams is 
still very low and the natives continue to drag their canoes from the 
head waters of one stream to those of the other. 
Several species of the family Loricariide, as well as some of the 
South American forms of the families Siluride, Characide and Cichlide, 
have found their way into the Rio Chagres. These seem to us to have 
reached this river before the last gap between the Rio Chagres and the 
streams of middle Panama was closed, rather than to have migrated 
directly from the Colombian streams. If this is the case, the last gap 
between the Chagres and one of the Pacific slope streams opposing it 
must have been closed earlier than the last passage between the Rio Tuyra 
and the Rio Atrato, for the similarity between the fishes of the two slopes 
in the region of the Canal Zone is not nearly so great as it is farther east- 
ward (Rio Atrato — Rio. Tuyra). It then is very probable that only 
the earliest migrants succeeded in reaching the Rio Chagres Basin. 
The representatives of the family Paeciliide may have entered 
Panama from Central America, as the majority of the species resemble 
Central American forms more than they do South American. The 
fresh water representatives of the family Mugilide have evidently 
migrated to this region from the north and reach the southern limit 
of their range in the Rio Chagres and the Rio Bayano. 
The fresh water species of the family Gobiide are more numerous 
in Panama than elsewhere. Most of them still frequent brackish water 
and it is probable that they evolved from marine shore forms, which 
have worked their way up streams and into fresh water. 
