peculiar freshwater forms on both sides of the Atlantic. Africa and South America are, moreover, the only continents which have produced in Freshwater fishes, though in very different families, one of the most extraordinary modifications of an organ--the conversion, that is, of muscle into an apparatus creating electric force. C. The boundaries of the TROPICAL AMERICAN (_Neotropical_) REGION have been sufficiently indicated in the definition of the Equatorial zone. A broad and most irregular band of country, in which the South and North American forms are mixed, exists in the north; offering some peculiarities which deserve fuller attention in the subsequent description of the relations between the South and North American faunæ. The following Freshwater fishes inhabit this region:-- Dipnoi [Australia, Africa]-- _Lepidosiren paradoxa_ 1 species. _Polycentridæ_ 3 „ Chromides [Africa]-- _Heros_, _Acara_, _Cichla_, etc. 80 „ (_Lucifuga_ 2 „) Siluridæ-- _Hypophthalmina_ 5 „ Pimelodina [Africa, 2 species] 70 „ Ariina [Africa, India, Australia, Fuegian] 35 „ Doradina [Africa] 60 „ Hypostomatina [India] 90 „ _Aspredinina_ 9 „ Nematogenyina [Fuegian]-- 2 „ Trichomycterina [Fuegian] 2 „ _Stegophilina_ 3 „ Characinidae [Africa]-- _Erythrinina_ 15 „ _Curimatina_ 40 „ _Anastomatina_ 25 „ Tetragonopterina 80 „ Hydrocyonina 30 „ Crenuchina 1 „ Serrasalmonina 35 „ Cyprinodontidæ-- Carnivoræ [Europe, Asia, N. America, India, Africa] 30 „ _Limnophagæ_ 31 „ Osteoglossidæ [Africa, India, Australia] 2 „ _Gymnotidæ_ 20 „ Symbranchidæ [India] 1 „ ------------ 672 species. ============