In the order Crocodilia, America has the peculiar family of the alligators (Alligatoridæ), as well as several species of true crocodiles (Crocodilidæ). The Chelonia (tortoises) are represented by the families Testudinidæ and Chelydidæ, both of wide range; but there are six peculiar genera,--_Dermatemys_ and _Staurotypus_ belonging to the former family,--_Peltocephalus_, _Podocnemis_, _Hydromedusa_, and _Chelys_, to the latter. Some of the Amazon river-turtles of the genus _Podocnemys_ rival in size the largest species of true marine turtles (Cheloniidæ), and are equally good for food. _Amphibia._--The Neotropical region possesses representatives of sixteen families of Amphibia of which four are peculiar; all belonging to Anoura or tail-less Batrachians. The Cæciliadæ or snake-like amphibia, are represented by two peculiar genera, _Siphonopsis_ and _Rhinatrema_. Tailed Batrachians are almost unknown, only a few species of _Spelerpes_ (Salamandridæ) entering Central America, and one extending as far south as the Andes of Bogota in South America. Tail-less Batrachians on the other hand, are abundant; there being 14 families represented, of which 4,--Rhinophryndæ, Hylaplesidæ, Plectromantidæ, and Pipidæ are peculiar. None of these families contain more than a single genus, and only the second more than a single species; so that it is not these which give a character to the South American Amphibia-fauna. The most important and best represented families are, Ranidæ (true frogs), with eleven genera and more than 50 species; Polypedatidæ (tree-frogs) with seven genera and about 40 species; Hylidæ (tree-frogs) with eight genera and nearly 30 species; Engystomidæ (toads) (5 genera), Bombinatoridæ (frogs), (4 genera), Phryniscidæ and Bufonidæ (toads), (each with 2 genera), are also fairly represented. All these families are widely distributed, but the Neotropical genera are, in almost every case, peculiar.