DISTRIBUTION AND LOCATION 267 



sub-family Catostomina are with one exception confined to this 

 continent ; Siluroids or cat-fishes are abundant, but it is a cur- 

 ious fact that they are confined to the regions east of the Rocky 

 Mountains ; the)' are known as channel-cats, Ictalurus, horned 

 pout, Amiurus, and mad-toms which are quite small and belong 

 to the genera Noturus and Sclribeodes. These Siluroids were 

 probably derived from South America. Cyprinodonts or 

 toothed carps are abundant in the more southern parts, the 

 range of this family having apparently extended from South 

 America since the Isthmus of Panama connected the two 

 continents; all the North American forms are carnivorous. 

 There are numerous species, and many of them are abundant 

 in individuals: the commonest genera are Cyprinodon, Gambusia 

 and Fiuidiilus, some species of the latter living on the sea-coast. 

 The Amblyopsidse, an offshoot from the Cyprinodonts including 

 the blind cave-fish and its allies, are peculiar to North America. 

 Of spiny-finned fishes (Acanthopterygii) the family Centrar- 

 chida; or sun-fishes are peculiar to North America and are 

 extremely abundant especially in the eastern rivers, the com- 

 monest genera are Lepomis and Micropterits, the latter known 

 as the black bass ; many of the species have a long backward 

 development of the gill-cover, above the upper angle of the gill- 

 aperture. 



Of the tropical continents we may take South America first 

 in order to contrast it with North America. Here there are no 

 Ganoids, but there is one species of lung-fishes (Dipnoi), namely 

 Lepidosiren paradoxus \ true carps are entirely absent, and their 

 place is taken by the Characinidae, elsewhere found only in 

 Africa ; Siluroids or cat-fishes are also very abundant (Plate 

 XXIII., B), several subfamilies being confined to this region 

 as Callichthyinae, Hypophthalminas and Trichomycterinae ; the 

 Loricariidae, which are specialised Siluridae, are also exclusively 

 South American, and likewise the Aspredinidae ; the Gymnotidre, 

 containing the electric eel and its allies which are related to the 

 Characinidae, are found nowhere else. Among the soft-finned 

 fishes (Malacopterygii) Osteoglossidae are represented by Osteo- 

 glossum and Arapaima. (Plate XXIII., A.) South America 

 is the head-quarters of the toothed carps (Cyprinodonts) of 

 which the herbivorous genera Poecilia, Mollienisia, Platypoecilus, 

 and Girardinus are found nowhere else. One species of Sym- 



