12 ZOOLOGICAL GEOGRAPHY. [pabt hi. 



Frcsh-7vatcr fishes.— The great rivers of Tropical America abound 

 in fish of many strange forms and pecidiar types. Three fami- 

 lies, and three sub-family groups are peculiar, while the number 

 of peculiar genera is about 120. The peculiar families are Poly- 

 centrida", with two genera ; Gymnotidaj, a family which includes 

 the electric eels, (5 genera) ; and Trygonidse, the rays, which are 

 everywhere marine except in the great rivers of South America, 

 where many species are found, belonging to two genera. Of the 

 extensive family Siluridte, three sub-families Siluridse anomalo- 

 pterse, S. olisthoptera;, and S. branchiolaj, are confined to this 

 region. The larger and more important of the peculiar genera 

 are the following : Percilia, inhabiting Chilian and Perciclithys 

 South Temperate rivers, belong to the Perch family (Percidae) ; 

 Acharnes, found only in Guiana, belongs to the Nandidse, a 

 family of wide range in the tropics ; the Chromidse, a family of 

 exclusively fresh-water fishes found in the tropics of the Ethio- 

 pian, Oriental and Neotropical regions, are here represented by 

 15 genera, the more important being Acara (17 sp.), Hews (26 

 sp.), Crenicichla (9 sp.), Satanoperca (7 sp.). Many of these fishes 

 are beautifully marked and coloured. The Silurida) proterop- 

 terre are represented by 14 genera, of which Pimelodus (42 sp.), 

 and Platystoma (11 sp.), are the most important; the Siluridse 

 stenobranchia3 by 11 genera, the chief being Doras (13 sp.), 

 Auchenvpterus (9 sp.), and Oxydoras (7 sp.). The Siluridaj pro- 

 teropodes are represented by 16 genera, many of them being among 

 the most singular of fresh- water fishes, clothed in coats of mail, 

 and armed with hooks and serrated spines. The following are 

 the most important, — Chcetostomus (25 sp.), Loriearia (17 sp.), 

 Plecostonus (15 sp.) and Gallichthys (11 sp.). The Characinidse 

 are divided between Tropical America and Tropical Africa, the 

 former possessing about 40 genera and 200 species. The Hap- 

 locliitonidae are confined to South America and Australia ; the 

 American genus being Haplochiton. The Cyprinodontida) are 

 represented by 18 genera, the most important being, Pcccilia (16 

 sp.), Girardinus (10 sp.), and Gambiisia (8 sp.) The Osteoglos- 

 sidfc, found in Australian and African rivers, are represented in 

 South America by the peculiar Arajjaima, the " pirarucu " of the 



