10 
ZOOLOGICAL GEOGRAPHY. 
[PABT III. 
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, Amblycephalidse, and Pythonidse, being those 
which are best represented by peculiar forms. There are 25 pecu- 
liar or characteristic genera, the most important berngDromicus 
(Colubridse) ; 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, 
Chirocolidee, Iphisiadse, and Cercosauridse ; but it must be noted 
that these all possess but a single genus each, and only two of 
them (Cbirocolidse and Cercosauridse) have more than a single 
species. The families which range over both South and North 
America are Chirotidse, Chaleidse, Teidse, 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 Iguanidse 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 
Teidse and Iguanidse, which thus especially characterize the 
region. The most important and characteristic genera are the 
following : Amciva (Teidse) ; Gymnopthalmus (Gymnopthalmidse) ; 
