INTRODUCTION. Xv 
not found on the Mexican Plateau, but in lowland rivers they extend northward to 
Sinaloa on the West and to the Rio Grande on the East. 
The South-American Acara and Geophagus are each represented by a single species 
in Panama. Most of the Mexican and Central-American Cichlide belong to the genus 
Cichlosoma, but usually to different sections of the genus from the South-American 
species. 
The section Theraps contains 21 species: 16 are from Guatemala and Mexico 
south of the Balsas, one of them ranging southwards to Panama; the most northern 
species occurs in the Panuco; whilst 3 are found in Lakes Managua and Nicaragua and 
1 in Costa Rica. 
Archocentrus comprises 6 species, 5 from Guatemala and Southern Mexico and 
1 from Lake Nicaragua. <Astatheros is made up of 4 species from Oaxaca, Guatemala, 
and British Honduras, 9 from the Great Lakes of Nicaragua, and 1 from Costa Rica and 
Panama. The 3 species of Thorichthys inhabit Guatemala and Southern Mexico. 
Parapetenia is the most widely distributed group of the genus Cichlosoma. 
In addition to the sixteen species known from Mexico and Central America there 
is one in Cuba and another in Barbados (the latter locality perhaps doubtful), two 
in Western Ecuador, one in Colombia, and one in the Amazon. The South-American 
species of this section are probably derived from immigrants from Central America. 
The Mexican and Central-American species of Parapetenia are distributed thus :— 
C. beani. Lowland streams of Sinaloa and Jalisco. 
C. istlanum. Rio Balsas. 
C. steindachneri and C. bartoni. Rio Panuco. 
C. mento, C. urophthalmus, C. centrale, C. tenue, C. trimaculatum, C. mojarra, 
C. salvini, C. multifasciatum, C. friedrichstahli, and C. motaguense. Southern 
Vera Cruz and Oaxaca to Guatemala. 
C. managuense and C. dovii. Jakes Managua and Nicaragua. 
Petenia is a monotypic genus, remarkable for the extremely protractile mouth, from 
Lake Peten. Herichthys, with four species from the Rio Grande to Lake Yzabal, differs 
from Cichlosoma in having incisor-like teeth. Paraneetroplus, with one species from 
Southern Vera Cruz and another from Costa Rica and Panama, and WNeetroplus and 
Herotilapia, each with a single species from the Great Lakes of Nicaragua, are allied 
genera. 
The points to be noted in the distribution of the Cichlid in Mexico and Central 
America are the following :—The chain of volcanoes which extends from Colima to 
Vera Cruz has checked the northward migration of the family, which is not repre- 
sented on the Mexican plateau. The majority of the species are found in Southern 
