100 



University of California Publications. 



[Geology 



Area microdonta belongs to the Monterey Miocene. 



A. montereyana ranges from the lower Monterey Miocene 

 through the middle and upper diviskms, and into the lower San 

 Pablo. It is very much more abundant in the middle Monterey 

 than elsewhere. 



A. canal is seems to extend from the middle San Pablo to the 

 middle Merced. 



A. trilineata is known in the San Pablo, though not certainly 

 in the lowest member, and seems to extend to a point somewhat 

 above the middle Merced. It is most abundant in the lower and 

 middle Merced. 



A. camuloensis is so far known from only a few localities, 

 occurring in strata probably referable to the Pliocene. 



Berkeley, California. 



November 30, 1901. 



