REPTILIA, BATRACHIA, AND PISCES. 115 
chin-shields from the four American species ; two of these, from Texas and California 
and from the West Coast of Mexico, differ in their scaling from the other more 
tropical species, one of which inhabits Panama and the other ranges from Costa Rica 
to Vera Cruz. 
The other families of Lizards found in America teach us nothing more than those 
dealt with above. There are several families common to the nearctic and neotropical 
regions, and most of these are found in other parts of the world also. South America 
is much richer in genera and species than North America; most of the Lizards of 
Central America north to the outer slopes of mountains that border the Mexican 
plateau belong to or are related to South American genera, and most of those found 
on the plateau are generically distinct from them, but in some cases (e. g. Sceloporus, 
Phrynosoma) only specifically so. 
There is not, on the whole, a very fundamental difference between the Lizard faune 
of North and South America; considering the differences in climate, and other 
features, we should expect most of the genera to be distinct, and in southern Mexico 
the transition from an elevated, dry, and almost treeless plateau bordered by mountains 
to a lowland district with tropical rainfall and vegetation accentuates this distinctness. 
But there are few differences that can be assigned definitely to the former isolation of 
the two continents, as practically nothing is known of the Tertiary history of the 
group. We know that some Mammalian genera, now tropical, formerly ranged 
further north and migrated from Asia to North America and thence to South America 
in late Tertiary times. Doubtless some Lizards, such as Mabuia, had a similar 
history ; but whether the Teiide, for example, were formerly nearctic, or whether 
they are for the first time spreading northwards, is a question difficult to answer. 
Snakes.—The burrowing snakes of the genus Typhlops have a wide distribution in 
the tropics; there are a few species in Mexico and Central America, and one of these 
is ZT. brahminus, collected by Dr. Gadow in Michoacan. Previously this species was 
known to range from Africa to China and on islands eastward to the Moluccas; 
probably it will be found on some of the islands of the Pacific. ‘This is an interesting 
parallel to the Gecko Gehyra mutilata ; in both cases Indian species have reached the 
West Coast of Mexico, and appear to have established themselves. The occurrence of 
Typhlops on oceanic islands indicates that the wide range of this genus is not due to 
its antiquity, but to susceptibility to accidental dispersal. 
Another genus of burrowing suakes, Glauconia, is found in America, Africa, and 
south-western Asia. (G. albifrons is tropical, ranging from Argentina to southern 
Mexico, but other species are found on the Mexican plateau and in the southern 
United States. 
The Boide show some points of interest. The Pythonine include a score of species 
from Africa, India, and Australia and a single American species, Loxocenus bicolor, 
Q 2 
