WEST COAST PLTLMONATA. 355 



WEST COAST PULMONATA; FOSSIL AND LIVING. 



BY J. G. COOPER, M. D. 

 Read March 21, 1 887. 



A. — Extinct Species. 



Since the publication of the article in Bulletin No. 4, 

 p. 235, several additional facts have been made known which 

 much increase our knowledge both of fossil and living 

 species. 



The most ancient known fossils of non-marine mollusca 

 in North xlmerica were those of the carboniferous strata of 

 Nova Scotia, and were of terrestrial forms. Some late dis- 

 coveries by the U. S. Geol. Survey "from the base of the 

 carboniferous of Nevada," give two fresh-water species, and 

 one of an amphibious or brackish-water type, allied to our 

 Alexia. (See "Science," II, p. 806, 1883, and Bulletin U. S. 

 Geol. Survey, No. 18, 1885.) These species show both a 

 wonderful similarity to living species, and an unexpected 

 variety of genera existing in what is so far the oldest land 

 fauna known. 



In the last-named Bulletin, Dr. White also figures an 

 extinct Unio and an extinct "Helix" (H. dalli Stearns, re- 

 ferred doubtfully to Mesodon) found in the John Day lacus- 

 trine basin of Oregon, together with three other species of 

 land-shells, of which two are inseparable from living spe- 

 cies now found only farther west, viz.: H. fidelis of Oregon, 

 and Gonostoma yatesll of California. The third is doubt- 

 fully referred to the eastern species Patida perspectiva. 



These are the most important evidences yet discovered of 

 the westward migration of the Pacific-slope species, being 

 now found only at 100 miles west and 500 miles south of 

 the locality of the fossils, in regions very different in cli- 

 mate, being far more moist. 



