252 CALIFORNIA ACADEMY OP SCIENCES. 



abundantly in the beds of the ravines beneath the volcanic 

 covering, from four thousand feet elevation down, in Plumas 

 County, also in Butte County in the foothills, it is most 

 probable that the shells exist there, though scarce or over- 

 looked. Calcareous tufa is also common in many places 

 where the limestone is not exposed, and quite as favorable 

 for land shells. These and other developments tend to show- 

 that the whole auriferous region is underlaid b}^ one if not 

 two strata of limestone, the lower one carboniferous, the 

 upper one, perhaps, Jurassic, cropping out on the east and 

 west edges. 



It is possible that the land shells, known by the Calaveras 

 skull specimen to have existed before the end of the vol- 

 canic overflow, may have been quite exterminated where 

 that covers most of the surface, and have not yet recolonized 

 the region, that formation being poorly suited for their pro- 

 duction. Several extra-limited forms have also been added 

 to the regions northward of California, as recorded by W. 

 G. Binney, in his " Supplements to Terr. Moll, of U. S. 



'7 



LlMAX OCCIDENTALIS, J. G. C. 



On a recent visit to Tehachipi Pass in May, 1885, I 

 searched carefully for land shells from 4,000 feet elevation, 

 down to about 600 on west slope, but found no traces of any 

 below the springy tract near summit, where this species 

 lives. 



Succinea Stketchiana, Bland. 



The only shell-covered terrestrial species seen in Tehachipi 

 Pass, along the upper part of that creek, in which also live 

 Limnophysa humilis Lea, Physa Blandii Lea, and Pisidium 

 occidentale Newe. There being plenty of limestone and 

 moisture there, it is strange that the large Helicoids, found 

 both north and south at the same elevations, do not occur. 



Others beyond our boundary are kindly reported to me by 

 Mr. F. E. Latchford, of Ottawa, Canada, as follows: "The 



