246 CALIFORNIA ACADEMY OF SCIENCES. 



established where the rivers cut through the coast range. I 

 have however thought it probable that the coast range may 

 have been colonized from the Sierra when the interior basin 

 was a lake. Two of the largest Sierra species, H. tudiculata 

 and H. Traskii, can be traced down to the coast southward 

 of lat. 35°, where the coast ranges are extensive and cut by 

 small rivers, while the latter, under the variety Diabloensis, 

 extends from there north almost the entire length of the 

 eastern slope of the coast mountains. Dr. Newcomb has 

 suspected that Mr. Thomson had some of the large var. 

 of H. Mormonum, found in the interior marshes, to confound 

 with the African Zonites, described by him as H. cultellata. 



But the fact of such marked variations from the Sierra 

 forms as occur in this and still more in others of the coast 

 range, proves at least a very ancient separation from the 

 same stock, if not a divergence of both from a common an- 

 cestry in the somewhat similar Oregon species. 



As bearing on this we also note that four large species 

 of the Rocky Mountains are scarcely distinguishable from 

 their representatives living in the Cascade Mountains of 

 Oregon, and show evidences of having been washed down 

 by branches of the Columbia River. A single colony of 

 Patula solitaria has been established on Government Island 

 in the Columbia Kiver, west of the Cascade Mountains, and 

 been found nowhere else on that slope. The interval be- 

 tween the mountain ranges above mentioned, in which no 

 species occur is about equal to the California valley, but 

 has no marshes in which they can find a home on the way. 

 In the California coast ranges, however, running north and 

 south, there are often two and sometimes three parallel se- 

 ries of forms, separable as species or sub-species. 



I have before attempted to show that a gradual succession 

 of species forming a chain, in which one form is observed to 

 pass into the next southward, either suddenly or by inter- 

 mediate links, can be traced from Oregon to ^Mexico, along 

 both ranges of Calif ornian mountains, but the connecting 



