SUBALPINE MOLLUSCA. 69 



iment and overgrown with rank aquatic grasses. The 

 water is very shallow and must follow very closely all 

 variations in the temperature of the air, which between 

 night and day are large. On the twenty-first of July the 

 temperature of the water at noon could not have been 

 below 50° or 55° Fah. A few days before we had expe- 

 rienced heav}- frosts nightly; the ponds were no doubt 

 correspondingly cold. 



As to the length of the season without ice I have no 

 direct evidence, but in conversation with Mr. Lembert 

 learned that he has been compelled to leave the mead- 

 ows for his winter quarters in Yosemite Valley, on ac- 

 count of deep snow, as early as October. The middle 

 of May of this year finds him still waiting in Yosemite 

 for the season to advance far enough to allow a retreat to 

 his home at Soda Springs. Ice forms in these shallow 

 ponds long before the heavy snow comes, and glazes 

 them nightly after the snow has melted. The Planorbis, 

 No. 13, and the Sfhceriuni, No. 18, were collected in 

 these ponds. 



The larger streams of the high Sierra are fed for 

 the greater part of the year by melting snow. Their beds 

 are hard granite or else are filled with bars of ijranitic 

 sand. Only in meadows overflowed by the spring fresh- 

 ets, or in shallow ponds, or in the warmer lakes and 

 smaller streams did I find traces of molluscan life. 



For comparison I may state that only numbers i. 4, 8, 

 12, 13, were found by me at Quincy, Plumas County, at 

 near 4,000 feet elevation. See Bulletin II, Cal. Acad. 

 Sci., p. 358, where three other land shells from there are 

 named. I also obtained there LiuuiopJixsa hiiniilis Say. 



