Dec. 28, 1916. FisHes or PANAMA— MEEK AND HILDEBRAND. 227 
well in the Chagres, as it is very rare there, nor has it undergone any 
changes different from those of the Pacific slope. Ancistrus chagrest, 
by whatever route it may have reached the Rio Chagres, is now abun- 
dant there and may also be regarded as one of the early migrants. It 
was found on the Pacific slope only in the small Rio Chorrera, the 
upper tributaries of which are opposite those of the Rio Trinidad. It, 
therefore, seems probable that this species crossed from one stream into 
the other before the gap between them became closed. The other 
representative of this family, Plecostomus plecostomus, is of wide dis- 
tribution and occurs on both slopes of Panama and southward. 
Among the characins evolution seems to be rather actively at work 
in a number of species. Brycon chagrensis, Brycon petrosus, 
Creagrutus notropoides and Reboides guatemalensis all have closely 
related opposites or relatives on the Pacific slope, but the influence of 
the different environment during their period of separation has brought 
forth certain definite and marked changes. Hyphessobrycon panamensis 
alone of all the characins from the Rio Chagres has no near relative 
elsewhere in Panama. The genus, however, reappears in Colombia. 
The Panama representative was probably one of the early migrants 
reaching the Chagres before the last passage between this river and the 
Pacific streams was closed. If it actually reached the Atlantic slope 
by that route, then we are obliged to conclude that the species was 
unable to maintain itself on the Pacific slope and while it became extinct 
there it thrived on the Atlantic. The rest of the species of the Chara- 
cide known from the Chagres are common to both slopes of Panama. 
Of these Astyanax ruberrimus at least also occurs throughout Colombia, 
and Hoplias microlepis while replaced by H. malabaricus in the Rio 
Tuyra Basin and in Colombia, oddly enough again reappears on the 
western slope of Ecuador. 
The single representative of the family Gymnotide is of wide dis- 
tribution, and does not appear to be undergoing any rapid changes. 
The representatives of the family Paciliide are common to both 
slopes, with the single exception of Gambusia nicaraguensis which can 
scarcely be regarded a fresh water form, as it seldom occurs above 
brackish water. 
Of the family Mugilide three species occur in the Rio Chagres. 
Two of them at least are common to both slopes of Panama and Central 
America as well as to the West Indies. 
Of the family Cichlide there are two species, Zquidens ceruleo- 
punctatus and Geophagus crassilabris, that are of rather wide distribution 
and are found everywhere in the streams of Panama. Cichlasoma 
maculicauda is found only on the Atlantic slope of Panama and north- 
