INTRODUCTION. XX1 
the two continents, but in at least one case (Brycon and Alestes) an American and an 
African genus are very closely allied. 
The Mexican and Central-American Characinide are evidently an offshoot from the 
South-American stock; as in the Cichlide, 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-American Characinide 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 Hoplias, two of Piabu- 
cina, one of Luciocharax, one of Gastropelecus, and one of Curimatus. 
2. Species belonging to South-American genera which extend further north than the 
Isthmus of Panama. ‘To this division belong two species of Brycon, one from 
Panama and Costa Rica, the other from Guatemala; a Leboides, ranging from 
Oaxaca to Ecuador; a Chirodon from the Rio Papaloapam ; and five species of 
Tetragonopterus, all closely allied to the widely distributed South-American 
T. rutilus. One species of Tetragonopterus is known only from Panama, a 
second ranges from Panama to Oaxaca and Vera Cruz, a third from Guatemala 
to Texas ; the other two are found in Southern Mexico. 
3. Two species belonging to the endemic genus Bramocharax, which appears to be 
related to Brycon and which is peculiar to the Great Lakes of Nicaragua. 
The GyMNoTID 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 
which (Giton fasciatus) extends from Guatemala to the La Plata, whilst a second 
(Eigenmannia humboldtiz) is found in Panama and Colombia. 
The Cyprinip& 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 anda few species are known from the Philippines 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 Characinide, from 
which they differ especially in the falciform lower pharyngeals. 
