INTRODUCTJOX. xxi 



the two continents, but in at least one case [Brijcon and Alesfes) an American and an 

 African genus are very closely allied. 



The Mexican and Central-American Characinida? are evidently an offshoot from the 

 South-American stock ; as in the Cichlidse, the immigrants have found the volcanic 

 chain of mountains which forms the southern boundary of the Mexican plateau an 

 impassable barrier to their northward progress, but in the Eastern lowlands they have 

 made their way as far north as the Rio Grande System. 



The Mexican and Central-Araei'ican Characinidae may be arranged thus : — - 



1. Species belonging to South-American genera, the northern limit of which is the 



Isthmus of Panama : in several cases these species occur also in Colombia or 

 Ecuador. To this division may be referred a species of Hoj>Has, two of Flulu- 

 cina, one of Luciocliarax, one of Gastropelecus, and one of Carimatus. 



2. Species belonging to South-American genera which extend further north than the 



Isthmus of Panama. To this division belong two species of Brijcon, one from 

 Panama and Costa Pica, the other from Guatemala; a Roehoulcs, ranging from 

 Oaxaca to Ecuador ; a Chirodon from the Rio Papaloapam ; and five species of 

 Tetragonojjtertis, all closely allied to the widely distributed South- American 

 T. rutilus. One species of Tetragonopterus is known only from Panama, u 

 second ranges from Panama to Oaxaca and Vera Cruz, a third from Guatemala 

 to Texas ; the other two are found in Southern Mexico. 



0. Two species belonging to the endemic genus Bramocliarax, which appears to be 

 related to Brycon and which is peculiar to the Great Lakes of Nicaragua. 



The Gymnotid.e are specialized eel-like Characinids, and have evidently evolved 

 from the latter in South America. There are about 8 genera and 30 species, one of 

 Avhich {Giton fasciatus) extends from Guatemala to the La Plata, whilst a second 

 {Eigenmannia humholdtii) is found in Panama and Colombia. 



The CvrRiNiD^ are fresh-water fishes of North America, Eurasia, and Africa. They 

 are absent from Madagascar and do not cross Wallace's Line ; the family is well 

 represented in Borneo and a few species are known from the Pliilippines and from 

 Bali, but none from Celebes or Lombok. In America they extend southwards to the 

 Rio Balsas in Southern Mexico and the Rio Usumacinta in Guatemala. 



The family is closely related to and probably derived from the Characinidae, from 

 Avhich they differ especially in the falciform lower pharyngeals. 



