1905. | AMPHIBIANS AND REPTILES. 243 
and from Neotropical groups, of both Amphibia and Reptilia, but 
no northern group has contributed, unless it had spread well into 
Central or even into South America (witness the Plethodonta, 
Anguide, Amphisbenide, Scincide, Xantusiide, Aglyphous 
Colubri ine, Iguanidee). 
All these Nearctic, or Old-Sonoran, groups must have been there 
in Miocene times. The same age must be assigned to the 
outhern immigrants—the Cystignathide, Hylide, Bufonide, 
Tejidee, Typhlopide. 
On the other hand, the following must be considered as 
decidedly post-Miocene so far as their existence in the present 
Central America is concerned: from the North the Pelobatide, 
Desmognathinee, and Amblystomatins, none of which extend, 
southwards, beyond Mexico proper; from the South the Engy- 
stomatinee, Opisthoglypha, KElapinee, none or few of which go 
beyond Mexico into the United States. Lastly, the latest arriv: als 
in South America are the Crotalins, of which only Lachesis 
lanceolatus has entered the Lesser Antilles. 
Ancient Sonorans are //eloderma and Chirotes. 
The Testudinidee are also Old Sonorans. Still with fair 
numbers in Mexico, but ever decreasing southwards through 
Central into South America, Testudo has arrived in Central and 
South America too late for the Antilles, but in time for the 
Galapagos. This indicates that the Caribbean Sea and Gulf of 
Mexico connection was established before the disappearance of 
the western extent of Central American land. It is another hint 
that the Isthmus of Panama is but the last vestige of a former 
much broader land-connection between the two Continents. 
Concerning the Colubrine Snakes, they remind us in their 
dispersal southwards of the Iguanide, Anguide, and Boide. 
They have gone in detachments. The earliest migrants, when 
arrived in South America, have developed there, and since, into 
Opisthoglypha and the Aglypha part 3; and these are now 
surging back, northwards, post-Antillean. A second lot are the 
Aglypha part 2, many of which have entered the Antilles. 
Lastly, the last detachment of northerners passing through 
Mexico and Central America, too late for the Antilles, but 
still continuing their southward migration. 
If I am right in the conclusion that American Colubrinze 
gave vise to Opisthoglypha in South America, it follows that 
Opisthoglypha are not a natural group, those of the Old World, 
chiefly paleotropical, being an instance of collateral development, 
convergent, spreads, or whatever term Aer be ean. ‘ed. 
and mace do not support it; on the Pecan their present distribution is 
opposed to it. 
About 70 species are known from Yucatan. Its fauna is essentially that of the 
Atlantic Tierra Caliente; it differs from that of the Antilles apparently by the 
-absence of Xantusiide, Glauconiide, and Anguide. On the other hand, it is incon- 
ceivable why Tortoises, Pit-vipers, Opisthoglypha, and Cnemidophorus, all of which 
are plentiful in Yucatan, should not have crossed over into Cuba if a direct land- 
bridge had been ay ailable. 
16* 
