SUBALPINE MOLLUSCA. 67 



with the typical eastern cam-pcstris, while northward it 

 runs into the sub-species hxpcrborcus of Westerhind from 

 Vancouver's Island to Alaska. 



In reviewing this list it will be noticed that the species 

 collected are naturally grouped into two divisions ; those 

 found on the west slope, 19 species, and those from the 

 eastern slope, 12 species, of which 9 also occurred on the 

 west slope, while 10 were found only on the west and 3 

 only on the east slope. While fewer species occurred on 

 the east, those found on both slopes reach higher eleva- 

 tions there, amounting to 2,000 or 3,000 feet more with 6 

 species and 4,000 to 5,000 in the case of two others. One 

 Pisidiiiin attained 700 feet higher elevation than any other 

 species, a fact noticed by Dr. Cooper of the same species 

 in latitude 39". And as it there lives about 2,000 feet be- 

 low the line of perpetual snow, it seems to have the same 

 relative elevation here, the snow-line in latitude 38^ being 

 given by the U. S, Geological Survey at 11,700 feet near 

 Mono Pass. 



The distribution of the terrestrial species is influenced 

 not only by the supply of moisture, but more strongly than 

 that of the aquatic by temperature, presence of lime and 

 suitable vegetation. Thus we found only aquatic shells 

 above 4,800 feet on the west slope and 8.000 feet on the 

 east. 



Lake Eleanor is bordered on its north-west shores by 

 an extensive flat, covered with meadow plants, thickets of 

 azalea and groves of pines. Ridges and boulders of ice- 

 polished granite traverse it near the lake, and between 

 these, parts of the meadow were still overflowed in June, 

 leaving ponds and mudholes in August. From these 

 damp groves and meadows the collections about the lake 

 were made. 



In Yosemite the terrestrial species were found near 



