396 PROCEEDINGS OF THE ACADEMY OF 



Triinorphodon and (?) Phimothyra. Elaps, extending westward to the Gulf 

 of California, has not yet been discovered at the Cape. 



No species has yet been found which is common to Cape St. Lucas and the 

 country of Vera Cruz and Jalapa. The genera common to both are Caudisona, 

 Drymobius, Thamnophis, Tropidonotus, Lampropeltis and Phimothyra ; all 

 found also in Texas and the Southern United States.* They form but one- 

 half of the whole number included in the Lucasian fauna. 



Genera characteristic of Jalapa, and not known to exist in Lower California, 

 Arizona, or Texas, are Catostoma, Ninia, Chersodromus, Pliocercus,t Steno- 

 rhina, Himantodes, Bothrops and Bothriechis ; all of which, except Cherso- 

 dromus, are represented in South America and intermediate localities. The 

 latter statement is true as regards Sibon, Coniophanes, and Spilotes, which 

 Jalapa shares with Texas, and of Arizona and Dryophis, which are found 

 in Sonora. Omitting Thamnophis and Lampropeltis as common to the two 

 faunae, we find here but one nearctic type (Tropidonotus) among the many neo- 

 tropical. 



We know but little of the herpetology of Guatemala west of the Cordilleras. 

 Caudisona d a r i s s a is the only serpent yet obtained there, which we suppose 

 to be found in Vera Cruz. The ten known genera are identical, excepting Loxo- 

 cemus, and ?Conophis. Other genera which have not been found north of Cen- 

 tral America, are Colobognathus, Hydrodipsas, Hydromorphus, Thamnocen- 

 chris, Dipsas, Tomodon, Xenodon, Scolecophis, Oxyrhopus ; the first four are 

 not known to extend into South America. Trimorphodon, Hypsiglena and 

 Tantilla, are the only genera known to be common to the fauna of Central 

 America and that of Lower California, Sonora and Arizona, which may be 

 called the Sonorian. 



Comparing this last subfauna with that of Southern Texas, at least five 

 degrees further south, we find that while neotropical genera are to nearctic in 

 the former in an equal proportion, in the latter they are as one to four. Of 

 five genera peculiar to the former region, four have neotropical representa- 

 tives, none nearctic. No genus is peculiar to the Texan region. Rhinochilus, 

 common and peculiar to the two regions, is nearctic in relationship. 



The probabilities are then, that the artificial line separating the neotropical 

 and nearctic groups of faunae must be placed several degrees further north 

 on the west of the Cordilleras than on the eastern coast region. It is also 

 probable that the tropic of cancer, the line proposed by Dr. Giinther, will be 

 found to be nearly the true position of its eastern extremity. 



List of the Mollusca inhabiting the neighborhood of Philadelphia. 



BY W. M. GABB. 



Believing that the best way of obtaining an accurate knowledge of the 

 geographical distribution of species, is by the publication of numerous local 

 lists, I have prepared the following catalogue of Mollusca of our neighborhood. 

 Most of the species have been collected by myself this season. I have received 

 valuable information and assistance from several of my friends, all of which 

 is acknowledged at the proper place. I have been careful to point out the 

 principal localities, more especially to assist young collectors. 



GASTEROPODA. 



MelaniidjE. 



Melania Virginic a Say. Found everywhere. The specimens from the 

 Schuylkill appear to be somewhat larger than those from the Delaware. 



* Phimothyra g rahamiae has been obtained at Port Mojave, California, by Dr. 

 Cooper, vid. Proc. Cal. Acad. Nat. Sci., 1861, p. 123 



t Is not this Elapochrus Peters ? A species inhabits New Grenada, and a third (P. 

 ac q u a 1 i s Salv.) eastern Guatemala. 



[Sept, 



