INTEODUCTIOX. XV 



not found on the Mexican Plateau, but in lowland rivers they extend northward to 

 Sinaloa on the AVest 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 Cichlidas belong to the genus 

 Cichlosoma, but usually to different sections of the genus from the South-American 

 species. 



The section Tlierajjs 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 Eica. 



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 ThorichtJiys inhabit Guatemala and Southern Mexico. 



Para])etema 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 oi Parapetenia are distributed thus: — 



C. beani. Lowland streams of Sinaloa and Jalisco. 



C. istlatium. Rio Balsas. 



C. steindackneri and C. bartoni. Rio Panuco. 



C. ijiento, C. urophihalmus, G. centrale, C. tenue, C. trimaculatum, C. mojarra, 



C. salvini, C. multifasciatum , C. friedrichstahli, and (J. motaguense. Southern 



Vera Cruz and Oaxaca to Guatemala. 

 C. managuense and C. dovii. Lakes 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 Neetroplus 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 Cichlidte in Mexico and Central 

 America are the following : — The chain of volcanoes Avhich 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 



