1889.] NATURAL SCIENCES OF PHILADELPHIA. 195 



ina; a barrier which was insurmountable to most land snails. From 

 the gradually receding Pacific, California, a narrow, long strip, 

 emerged. Sometime in the early tertiary (probably ) there was an 

 infusion of Palsearctic types into this region, from the Northwest. 1 

 To this influence we owe the Arionta-like shells, Gonostoma, Ario- 

 limax (most nearly related to the Old World genus Arion), etc., 

 which are closely allied to characteristic Palsearctic types, but ai*e 

 quite different from the snails of Eastern North America. 



(4.) American fauna, embracing the whole country lying East of 

 the Sierra ^Nevada range. This is the autochthonous American 

 fauna, developed with very little trace of Old World influence, or 

 none at all, from an early, probably Cretaceous, period. Characteristic 

 groups are Jlesodon, Stenotrema, Triodopsis, Polygyra, Strepoma- 

 tidoe, Campeloma, Amnicola, Somatogyrus, etc. 



In the South this fauna has received species from two sources: (5) 

 Mexican species, such as Bulimulus alternatus and schiedeanus, Holo- 

 spira, etc., and (6) West Indian and Central and South American 

 forms which have passed into Florida, such as Orthalicus, Liguus, 

 Bulimulus Oylindrella, Microphysa, Ptychopatula, etc. The number 

 of these makes it probable that there has been land connection with 

 South America by way of the Antilles and Caribees ; a theory which 

 derives no slight support from the finding in Florida of quaternary 

 fossil Glyptodon and other South American forms. 2 



Family i. TESTACELLIDJE. 

 Genus i. GLANDINA Schumacher, 1817. 



1. Glaxdixa truxcata Gmel. Coast Region from Ga. and 



Fla., to Texas, 

 la. Glaxdixa truxcata bullata Gld. Louisiana, 

 lb. Glaxdixa truucata parallela W. G. Binney. Florida. 



2. Glaxdixa texasiaxa Pfr. Brownsville, Texas. 



3. Glaxdixa decussata Desh. Central Southern Texas. 



4. Glaxdixa vanuxemensis Lea. Southern Texas. 



Family ii. SELENITIDJE Fischer. 

 Genus ii. SELENITE3 Fischer, 1878. 



•3. Selexites coxcava Say. Eastern U. S. 

 6. Selexites vaxcouverexsis Lea. Washington Ter., to 

 Alaska ; Western Idaho. 



i Siberia and Alaska are now united by a ridge covered by less than 50 

 fms." depth. This was probably dry land during the Eocene, as it is also said to 

 have been during part of the Quaternary. 



2 See Proc. Acad. X. S. Phila. ]88'J, p. 96. 



