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Show 1905.] AMPHIBIANS AMD REPTILES. 243 ancl from Neotropical groups, of both Amphibia and lleptilia, but no northern group has contributed, unless it had spread well into Central or even into South America (witness the Plethodonta, Anguidse, Amphisbsenidse, Scincidfe, Xantusiidse, Aglyphous Colubrina?, Iguanidse). 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 Cystignathidse, Hylida?, BufonicUe, Tejidse, Typhlopidse. 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 Pelobatidfe, Desmognatliinae, and Amblystomatime, none of which extend, southwards, beyond Mexico proper; from the South the Engy-stomatinse, Opisthoglypha, Elapime, none or few of which go beyond Mexico into the United States. Lastly, the latest arrivals in South America are the Crotalinae, of which only Lachesis lanceolatus has entered the Lesser Antilles. Ancient Sonorans are Heloderma and Chirotes. The Testudinidfe 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 Iguanidse, Anguidse, and Boidfe. 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 Colubrime gave rise to Opisthoglypha in South America, it follows that Opisthoglypha are not a natural group, those of the Old World, chiefly palseotropical, being an instance of collateral development, convergent, homoplastic, or whatever term may be preferred. and Reptiles do not support it; on the contrary, 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 Xantusiida?, Glauconiidse, and Anguidse. On the other hand, it is inconceivable 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 available. 1 6 * |