10 ZOOLOGICAL GEOGKAPHY. [part hi. 



altogether peculiar families, and several others which only range 

 into the Nearctic region, as well as a very large number of pecu- 

 liar or characteristic genera. As the orders of reptiles differ 

 considerably in their distributional features, they must be con- 

 sidered 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 Neotrop- 

 ical possesses no peculiar family, nor even one confined to the 

 American continent. The families of most restricted range are — 

 the Scytalidse, only found elsewhere in the Philippine islands ; 

 the Amblycephalidse, common to the Oriental and Neotropical 

 regions ; and the Tortricidee, 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 Colubridse, Amblycephalida?, and Pythonidse, being those 

 which are best represented by peculiar forms. There are 25 pecu- 

 liar or characteristic genera, the most important being Dromt'cws 

 (Colubridffi) ; Boa, Epicrates, and Ungalia (Pythonidse) ; Elaps 

 (Elapidse) ; and Craspedocephalus (Crotalidse). 



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 Helodermidse, Anadiadse, 

 Chirocolidse, Iphisiadse, and Cercosauridse ; but it must be noted 

 that these all possess but a single genus each, and only two of 

 them (Chirocolidse and Cercosauridse) have more than a single 

 species. The families which range over both South and North 

 America are Chirotid*, Chalcidse, Teidae, and Iguanidse; the 

 first and second are of small extent, but the other two are very 

 large groups, the Teidse possessing 12 genera and near 80 species; 

 the Iguanidffi 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 

 Teid« and Iguanidae, which thus especially characterize the 

 region. The most important and characteristic genera are the 

 following : Ameiva (Teidffi) ; Gymnopthalmus (Gynmopthalmidse) ; 



