REPTILIA, BATRACHIA, AND PISCES, 107 
Alestes of the Characide, and of Acara and Paratilapia of the Cichlid, seems 
apparent. Further support is derived from the Lepidosirenide, with Lepidosiren in 
South America and Protopterus in Africa, and from the relationship of the Pimelodide 
and Bagride. 
Evolution and Dispersal of Neotropical Fishes.—Since all the genera and 
most of the families of true fresh-water fishes of the Neotropical Region are peculiar, 
and the majority of the endemic families may be regarded as specialized Characide 
or Pimelodide, it may be inferred that the present fish-fauna has evolved in South 
America from a few ancestral types, and that it has received no immigrants from other 
regions since the earliest of the Tertiary. 
It is generally accepted that the Antillean Region was submerged during the Eocene, 
and that the invasion of Central America from the south dates back not earlier than 
the Miocene. The distribution of the fishes is in harmony with this supposition, for, 
whilst most of the Neotropical families have a wide range in South America, only four 
of them extend north of the isthmus of Panama. One of these is the Gymnotide, 
represented by Gymnotus carapo (Giton fasciatus), found everywhere from Montevideo 
to Guatemala; the others are the Pimelodide, Characide, and Cichlide. The 
_ Pimelodide are represented mainly by about twenty species of the large and widely 
distributed South American genus Lhamdia, which ranges north on the Atlantic side 
to southern Vera Cruz, but has not reached the Balsas nor the Mexican Plateau. 
A few genera of the Characide have got as far as Rhamdia, and it is only two or 
three forms that are scarcely specifically distinct from Tetragonopterus (Astyanaz) 
rutilus, found everywhere in South America north of the La Plata, that extend the 
range of this family to the Balsas and on the Atlantic slope to the Rio Grande. 
In the Characide and Pimelodide invasion of Central America has resulted in the 
differentiation of a number of species, but has produced no types that are markedly 
distinct from their relatives in South America. 
The Cichlide are in many respects peculiar; the Central and South American 
species are about equal in number and for the most part are generically or at least 
subgenerically distinct, so that it is usually possible to recognize at a glance whether 
a species is Central or South American. The South American types are the more 
generalized, for the majority have three anal spines and simple conical teeth ; in the 
Central American genera the number of anal spines is increased and various 
specializations of the dentition occur. The great lakes of Nicaragua have a highly 
specialized endemic Cichlid fauna; many species are found in the region between 
Panama and southern Vera Cruz, and a few in the Atlantic coast-streams northwards 
to the Rio Grande. Only one species, belonging to the genus or subgenus Parapetenia, 
is found in the Balsas and a related form in the lowland streams of Sinaloa; a species 
of this type also occurs in Cuba. The Central American Cichlide are a difficult group 
P2 
