368 CALIFORNIA ACADEMY OF SCIENCES. 



Contra Costa and Alameda Counties. 



These two counties form a quadrangle, including the 

 whole region " East of San Francisco Bay," and are about 

 40 miles square. About 270 square miles of the eastern 

 portion, rising from the level marshes up to about 200 feet, 

 is very arid in summer, the water-courses nearly all dry- 

 ing up, and no trees growing along their banks for 10 or 15 

 miles. The river shores south of the westward bend, are, 

 however, lined by large trees and shrubbery, where not too 

 marshy, and Avould no doubt support many species washed 

 down to them, if the floods, both of summer and winter, 

 did not destroy those that escape tramping cattle. 



Only two species have been found living near the marshes, 

 Nos. 25 and 32, besides the four amphibious Succineas, 42, 

 43, 44 and 45. 



At the foothills near Mt. Diablo, water begins to be per- 

 manent in pools, and above the porous sandstones is found 

 running in summer down to about 100 feet above tides, 

 wherever the harder metamorphic rocks occur, while trees 

 again become common along the streams, and in cool, 

 springy situations live-oaks, pines and shrubbery cover parts 

 of the hillsides. On the north slopes, and always near fos- 

 sil if erous rocks between 100 and 1,000 feet elevation, are 

 found small colonies of No. 32. From a similar locality on 

 the east slope, Prof. Brewer brought the type of No. 37. 

 I searched carefully on the south and west slopes, but 

 could find none of any kind in the best localities, nor was 

 Dr. Yates more successful in a careful examination of the 

 ridge 10 or 12 miles S. E. of the peak. None were found 

 above 1,000 feet for 5 miles up the north slope, where little 

 lime and no fossils occur, and though these are found 

 over 2,000 feet on the south side, the greater heat apparent- 

 ly prevents the existence of any except Limacoid species. 



But as some of these are found active in wet places 

 through the dry season, and dead shells always show the 

 existence of other kinds when not active , it seems unlikely 



