CALIFORNIA ACADEMY OF SCIENCE.-. 235 



ON FOSSIL AND SUB-FOSSIL LAND SHELLS OF 

 THE UNITED STATES, WITH NOTES ON LIV- 

 ING SPECIES. 



By J. G. Cooper, M. D. 



1. EXTIXCT SPECIES 



In a former article I attempted to trace back the origin of 

 our Land Shells to their fossil ancestry, showing that 

 they very probably descended from species known to be 

 eocene, in Nebraska; and quite possibly from still older 

 forms once existing in the northern part of this continent, 

 or of an older Arctic continent. Notes on the same subjects 

 are scattered in papers published by me in the Ann. N. Y. 

 Lye. N. H., VIII, 1861; Proc. Cal. Acad. Sc, III to VI, 

 1864 to 1875; Amer. Jour, of Conch., IV to VII; 1869 to 

 1871; Proc. Phil. Acad. N. Sc, 1872; and Proc. Amer. 

 Phil. Soc, XVIII, 1879. 



In the Third Annual Eeport of the U. S. Geol. Survey for 

 1882, pp. 453, 475, Dr. C. A. White goes so far as to refer 

 fossil species from Nebraska and from the eocene of the 

 Eocky Mountains to the same divisions of the land shells as 

 now exist on the west slope, including ten divisions, besides 

 two Pupillse and a Succinea, as well as three Bulimoid species 

 of more southern forms, different from those mentioned by 

 me in the Am. Jour, of Conch., IV, 212, as occurring near 

 Carson Valley, Nevada. 



Of the ten forms mentioned, only two are like those now 

 living near the Eocky Mountains, three or four extinct, and 

 the rest allied to species now found only west of the Sierra 

 or Cascade Eange. This confirms my previous theory that 

 the latter are descended from an original stock, living north 

 and east of California. It is also interesting to find that so 

 many marked divisions of the original stock existed as far 



5— Issued October 13, 1885. 



