158 SHELLS OF LOWER CALIFOBNIA— STEARNS. vol.xvii. 



DENTALIITM SEMIPOLITUM, Carpenter. 



Numerous specimens. 



Mulege Bay (Nos. 46201, 46202, U. S. N. M.); Bocadelos Piedras 

 (No. 46203, U. S. N. M.). Hemphill has collected this species at San 

 Ignacio Lagoon, Lower California (No. 105517, U. S. N. M.). 



Class GASTROPODA. 



Family B u l l i d ^. 



BULLA ADAMSI, Meuke. 



Several specimens. 



Bocas de los Piedras and Loreto, Gulf of California. 

 Less globose and inclined to be heavier and more solid than B. nehu- 

 losa Gould. The latter averages much larger than B. adamsi. 



Family AplysiidyE. 



DOLABELLA CALIFOKNICA, Stearns. 



DolaheUa californica, Steahns, Proc. Phila. Acad. Nat. Sci., 1878, p. 39.5, PI. vii, 

 figs. 1,2; Proc. U. S. Nat. Museum, Vol. xvi, pp. 341-342, 1892. 



Several examples (No. 75001, U. S. N. M.). Mulege Bay, Gulf of 

 California. 



Supei-family JVLONOTREMATA. 



Family H E l i(! i D ^. 



HELIX (ARIONTA) AKEOLATA, Forbes. 



= Euparypha'' areolata, Binnry. 



Abundant (No. 58470, U. S. N. M.). Santa Maria Island, Lower 

 California. 



'Whatever may be the subgeneric or sectional value of Euparypha, I do not 

 believe that any of the West American sjjecies can properly be assigned to it. 

 Environmental influences have brought about certain external facies analogous to 

 those exhibited by some of the terrestrial species that inhabit the Mediterranean 

 region, the Canaries and Madeira, wbere, to a certain extent, similar enviroumeutal 

 factors exist. 



I regard all of tlie west coast forms to which the names of Tryoni, areolata, Veatchii, 

 pandora, Iwvis, etc., have been given as physiographical aspects or modifications of 

 Arionta, as this genus is represented on the west coast by the more northerly and 

 characteristic forms of central California, generally placed by systematists in H. and 

 A. Adams's section Lysinae. 



Proceeding southerly from the regions of maximum or moderate rainfall or 

 humidity the extremes of external characters, exhibited by the Helices of southern 

 California and the peninsula, in color, solidity, elevation, etc., and general facies, 

 when compared with their congeners of the central region, seem to me, when a 

 large geographical series is examined, to be gradually apjiroached. We should 



