1904.] 



NATURAL SCIENCES OF PHILADELPHIA. 



467 



presence of pleurodire turtles in South America, and of two genera of 

 Neotropical Boida3 in Madagascar. It has been showai by Heer, in 

 his researches upon Arctic fossil plants, that in the process of secular 

 cooling the mean temperature of northern Greenland, as late as the 

 early Miocene, was not far removed from that of central Virginia at 

 the present time — quite warm enough for the needs of such hardy stocks 

 as the genera above named — and the differentiation of reptiles of 

 modern types" had progressed so far by the close of the Mesozoic, that 

 not much risk is incurred in believing that many existing genera were 

 in existence long before the end of the Eocene. Assuming a north 

 Atlantic highroad to have been the means of communication, the 

 longest Nearctic establishment of these common forms is likely to 

 have been in the older geological regions far in the east. It is further 

 true that with many of them traces of their primitive representatives 

 appear to be found in existing species of the eastern part of the Austro- 

 riparian. 



Omitting mere Neotropical intrusions into the southern border of 

 the Nearctic, such as Alligator, Crocodilus, Anolis, Sphcerodactylus , 

 Helicops, Spilotes, Rhadinea, Drymobius, Tantilla, ErytJirolamprus 

 and Elaps, as well as Trionyx, Chelydra, Emys and Testudo, each of 

 which had a wide Tertiary extension in northern regions, but whose 

 recent distribution throws no further light on the present question, 

 most of the remaining genera may be referred for their origin to the 

 Austroriparian or Lower Sonoran faunas. 



A ustroriparian : 



Macroclemmys 



Aromochelys 



Cinosternum 



Chrysemys 



Malaclemmys 



Terrapene 



Ophisaurus 



Liolepisma 



Rhineura 



Eutoenia 



Tropidonotus 



Seminatrix 



Storeria 



Clonophis 



Tropidocloniiim 



Haldea 



Amphiardis 



Coluber 



Zamenis 



Cyclophis 



Liopeltis 



Diadophis 



Ophibolus 



Stilosoma 



Carphophis 



Farancia 



Abastor 



Virginia 



Cemophora 



Heterodon 



Ancislrodon 



