1905.] AMPHIBIAXfS AXD EEPTILES. 243 



and from Neotropical groups, of both Amphibia and Reptilia, but 

 no northern group has contributed, unless it had spread Avell into 

 Central or even into South America (witness the Plethodonta, 

 Anguidse, Amphisbsenidee, Scincidfe, Xantusiidos, Aglyphous 

 Oolubrinaj, Iguanidee). 



All these Nearctic, or Old-Sonoran, groups must have been there 

 in Miocene times. The same age must be assigned to the 

 outhei'n immigrants — the Cystignathidse, Hylidse, Bufonidse, 

 Tejidfe, Typhlopid,*©. 



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 jSTorth the Pelobatidae, 

 Desmognathinse, and Amblystomatinse, none of which extend, 

 southwards, beyond Mexico proper; from the South the Engy- 

 stomatinse, Opisthoglypha, Elapinfe, none or few of which go 

 beyond Mexico into the United States. Lastly, the latest arrivals 

 in South America are the Crotalinfe, of which only Lachesis 

 lanceolatus has entered the Lesser Antilles. 



Ancient Sonorans are Heloderma and Chirotes. 



The Testudinidse 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, Anguidfe, and Boid?e. 

 They have gone in detachments. The eailiest 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 northeniers passing through 

 Mexico and Central America, too late for the Antilles, liut 

 still continuing their southward migration. 



If I am right in the conclusion that American Colubi-inje 

 gave rise to Opisthoglypha in South America, it follows that 

 Opisthoglypha are not a natural group, those of the Old World, 

 chiefly pal?eotropical, being an instance of collateral development, 

 convergent, homoplastic, or whatever term may be preferred. 



and Reptiles do not support it; on the contraiy, their present distribution is 

 opposed to it. 



About 70 species are known from Yucatan. Its fauna is essentiall3' that of the 

 Atlantic Tierra Caliente; it differs from that of the Antilles apparent!}'- by the 

 absence of Xantusiida?, Glauconiidaj, and Anguidte. On the other hand, it is incon- 

 ceivable why Tortoises, Pit-vipers, Opisthoglypha, and Cnemidophoriis, all of which 

 are plentiful in Yucatan, should not ha\'e crossed over into Cuba if a direct land- 

 bridge had been available. 



16* 



