_Reptiles._--The Neotropical region is very rich in varied forms of reptile life, and the species are very abundant. It has six {10}altogether peculiar families, and several others which only range into the Nearctic region, as well as a very large number of peculiar or characteristic genera. As the orders of reptiles differ considerably in their distributional features, they must be considered separately. The snakes (Ophidia) differ from all other reptiles, and from most other orders of vertebrates, in the wide average distribution of the families; so that such an isolated region as the Neotropical possesses no peculiar family, nor even one confined to the American continent. The families of most restricted range are--the Scytalidæ, only found elsewhere in the Philippine islands; the Amblycephalidæ, common to the Oriental and Neotropical regions; and the Tortricidæ, most abundant in the Oriental region, but found also in the Austro-Malay islands and Tropical South America. Sixteen of the families of snakes occur in the region, the Colubridæ, Amblycephalidæ, and Pythonidæ, being those which are best represented by peculiar forms. There are 25 peculiar or characteristic genera, the most important being _Dromicus_ (Colubridæ); _Boa_, _Epicrates_, and _Ungalia_ (Pythonidæ); _Elaps_ (Elapidæ); and _Craspedocephalus_ (Crotalidæ). The lizards (Lacertilia) are generally more restricted in their range; hence we find that out of 15 families which inhabit the region, 5 are altogether peculiar, and 4 more extend only to N. America. The peculiar families are Helodermidæ, Anadiadæ, Chirocolidæ, Iphisiadæ, and Cercosauridæ; but it must be noted that these all possess but a single genus each, and only two of them (Chirocolidæ and Cercosauridæ) have more than a single species. The families which range over both South and North America are Chirotidæ, Chalcidæ, Teidæ, and Iguanidæ; the first and second are of small extent, but the other two are very large groups, the Teidæ possessing 12 genera and near 80 species; the Iguanidæ 40 genera and near 150 species; the greater part of which are Neotropical. There are more than 50 peculiar or highly characteristic genera of lizards, about 40 of which belong to the Teidæ and Iguanidæ, which thus especially characterize the region. The most important and characteristic genera are the following; _Ameiva_ (Teidæ); _Gymnopthalmus_ (Gymnopthalmidæ); {11}_Celestus_ and _Diploglossus_ (Scincidæ); _Sphærodactylus_ (Geckotidæ); _Liocephalus_, _Liolæmus_, _Proctotretus_, and many smaller genera (Iguanidæ). The three extensive Old World families Varanidæ, Lacertidæ, and Agamidæ, are absent from the entire American continent.