12 
ZOOLOGICAL GEOGRAPHY. 
[part m. 
Fresh-water fishes . — The great rivers of Tropical America abound 
in fish of many strange forms and peculiar 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- 
centridas, with two genera ; Gymnotidse, a family which includes 
the electric eels, (5 genera) ; and Trygonidse, the rays, which are 
every where marine except in the great rivers of South America, 
where many species are found, belonging to two genera. Of the 
extensive family Siluridae, three sub-families Siluridae anomalo- 
pterae, S. olisthopterae, and S. branchiolae, are confined to this 
region. The larger and more important of the peculiar genera 
are the following : Per cilia , inhabiting Chilian and Pereichthys 
South Temperate rivers, belong to the Perch family (Percidae) ; 
Acharnes , found only in Guiana, belongs to the Nandidae, a 
family of wide range in the tropics ; the Chromidae, 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.), Keros (26 
sp.), Crenicichla (9 sp.), Satanoperca (7 sp.). Many of these fishes 
are beautifully marked and coloured. The Siluridae proterop- 
terae are represented by 14 genera, of which Pimdodus (42 sp.), 
and Platy stoma (11 sp.), are the most important; the Siluridae 
stenobranchiae by 11 genera, the chief being Boras (13 sp.), 
Auchenipterus (9 sp.), and Oxydoras (7 sp.). The Siluridae 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 , — Ghcetostomus (25 sp.), Loricaria (17 sp.), 
Plecostonus (15 sp.) and Callichthys (11 sp.). The Characinidse 
are divided between Tropical America and Tropical Africa, the 
former possessing about 40 genera and 200 species. The Hap- 
lochilonidse are confined to South America and Australia ; the 
American genus being HaplochUon. The Cyprinodontidse are 
represented by 18 genera, the most important being, Poecilia (16 
sp.), Girardinus (10 sp.), and Gambusia (8 sp.) The Osteoglos- 
sidse, found in Australian and African rivers, are represented in 
South America by the peculiar Arapaima, the “pirarueu” of the 
