512 CALIFORNIA ACADEMY OF SCIENCES. 



sider this as merely analogical, caused by the general law 

 before stated, that the varieties of each group are more de- 

 pressed and umbilicate the farther from the coast. Thus 

 we find No. 32 passing into higher forms of 30 to the west, 

 and one variety between 30 and 31 is imperforate though 

 depressed. In the same way C. trashii and 37 pass into 38 

 and 39 near Monterey bay. 



A similar effect of climate is observed in the passage of 

 No. 28 toward 26, 27, and 29, in the cooler moister regions 

 west and north, and perhaps into 35 southward. The vari- 

 eties 30 to 34 seem to have diverged from 33 (or 32) east of 

 the bay, though 30 and 34 are now more abundant on the 

 west side. No. 41 seems also the coast form of No. 40. 

 On the other hand No. 6 may have varied into 7 and 8, which 

 are not known westward. No. 11 seems to have changed 

 into 13 and 14 toward the dry east and south slopes, while 

 36 has before been traced by intergrades to C. Jidelis, the 

 northern form as old as miocene times. 



XI. The greater extent of both salt and fresh waters 

 through the Bay region, in early quaternary times, no doubt 

 caused a more moist and uniform climate to prevail through- 

 out the Bay region, and was more favorable to the growth 

 and diffusion of Pulmonata than the present epoch. Then 

 the conditions were similar around Livermore Valley to 

 those of Monterey now, and to this I attribute the existence 

 there of No. 34, a few of which still survive toward Cedar 

 Mountain. 



XII. In the article on tlie ''Influence of Climate and 

 Topography on our Trees," (Proc. Cal. Acad. V. 285, 1874), 

 relating to the same region included in the map now given, 

 I showed that very few species occurred in San Francisco 

 County, while they increase in numbers of both species and 

 individuals up to 60 miles in nearly all directions. This 

 was attributed to the violence of the summer winds near the 



