362 CALIFORNIA ACADEMY OF SCIENCES. 



the top of the Coast range that they receive more moisture 

 in winter and are no drier in summer, but the foothills be- 

 low 3,000 feet are both hotter and drier. It thus happens that 

 most of the land shells are to be found from that elevation 

 up to 6,000 feet, and though washed down by the streams, 

 can only exist in the foothills, in places either marshy or 

 springy, or sheltered by rocks, trees and caverns. 



But we find two of them, Nos. 5 and 6, of the last list, 

 becoming common down to the sea in the counties south of 

 lat. 35°, the valleys there being open to the sea breeze and 

 less heated or dried up in summer, although the annual rain- 

 fall is much less than in the Sierras. They there attain their 

 greatest perfection, and No. 5 becomes much varied, assuming 

 forms on the islands, claimed to be distinct species. Fol- 

 lowing No. 5 toward the northwest it changes still further, 

 for near Point Conception Dr. Yates obtained a form of large 

 size but with nearly the same dark color as that of H. du- 

 2)etitJiouarsi combined with the sculpture of H. traski. It has, 

 in fact, nearly the same size and form as the figure of the 

 former copied by Binney from Deshayes, but which was de- 

 scribed as colored like H, fidelis. 



Fifty miles farther north Mr. Kaymond found a form like 

 No. 5 in color but with the wrinkled epidermis of the Mon- 

 terey shell, and at San Simeon, 90 miles north, smaller speci- 

 mens exactly like those from Monterey. So there is here a 

 transition by graded varieties between the two, much as in 

 the links connecting fidelis with infumata near Humboldt 

 Bay. Still there is a geographical limitation of each lead- 

 ing form, indicating the probability that these links may be 

 hybrids, or not truly species, they being very variable, while 

 the species are quite uniform over wide tracts of country. 

 They are parallel cases to the numerous varieties of 

 Patida s^ri^osa, which within a limited range are found in great 

 numbers, so variable in size, form, color, and sculpture, 

 that scarcely two are alike. 



These discoveries extend the range of H. dapetUhouarsi 



