REPTILIA, BATRACHIA, AND PISCES. 113 
(Liopelma), indicates that in all probability some of the Batrachian families are more 
ancient than those of fresh-water fishes. There seems no reason to doubt that they 
can and have spread rapidly, but probably their main distribution was accomplished 
before the Tertiary. The Urodela have in all probability always been northerners, 
and have only recently penetrated into South America. ‘The Cecilians are tropical, 
but their absence from the Australian Region rather tells against the idea that they 
are a very ancient group. Many families of the Anura are widely distributed 
and probably ancient; the Cystignathide and Hylidae seem to be old neotropical 
families. 
REPTILIA. 
Reptiles.—Leaving out the aquatic members of this group, some Reptiles can and 
do swim across the sea; others that are arboreal or that burrow into or hide in trunks 
of trees are peculiarly liable to accidental transmission over the ocean. Nearly all 
can travel quickly overland, so that in all probability the dispersal of many groups 
has been accomplished rapidly. The difference between the Nearctic and Neotropical 
regions is decidedly less marked than in the Batrachians, but the boundary is 
the same. 
Of the groups of Reptiles represented in Central America the Crocodiles and 
Tortoises are ancient and seem to have been cosmopolitan at the beginning of the 
Tertiary ; a study of their present distribution leads to no very important results. 
The Lizards and Snakes are the dominant orders of the present day, but their past 
history is almost unknown; in all probability the principal families date back to early 
FKocene times, and as they developed during the Tertiary they may have used the same 
routes of migration as the Mammalia. 
Dr. Gadow’s papers on the Reptiles and Batrachians of Mexico and Central 
America have been referred to above (p. 59) and are of great interest, especially 
when they deal with the effects of altitude, climate, terrain, etc., on the distribution ; 
his deductions as to the origin and migrations of the different groups are necessarily 
based mainly on their present distribution, and are to that extent unsatisfactory. The 
Mammals, whose evolution during the Tertiary, extended migrations, survivals, and 
extinctions are very thoroughly known for several orders, teach that it is very unsafe 
to deduce centres of origin and dispersal from present distribution alone. — 
Lizards.—There appear to be no families of Lizards restricted to South America, 
but most of the 35 genera of one family, the Teiide, are peculiar to that continent ; 
half a dozen South American genera range into Central America, two reaching 
southern Mexico, and one—Cnenudophorus—the United States. This genus includes 
, species on the Mexican plateau, as well as in the lowland forests. ‘The conclusion 
that this is an old neotropical family seems not unreasonable, but may be incorrect ; 
the neotropical Monkeys furnish a parallel. | | 
BIOL. CENTR.-AMER., Introd. Vol., June 1915. Q 
