A NEWMOLLUSK OF THE GENUS PISIDIUM FROM ALASKA, 

 WITH FIELD NOTES BY G. DALLAS HANNA. 



By Victor Sterki, 



Of New Philadelphia, Ohio. 



NOTES ON HABITS AND LIFE HISTORY. 



The Pribilof group of islands, noted for its fur-seal herds, is located 

 in Bering Sea about 200 miles from land on the north, east, and south. 

 St. Paul and St. George are the largest and most important of the 

 group and are the only ones having bodies of fresh water. 



St. George Island has several small, shallow ponds of typical arctic 

 tundra character, the banks of which are composed of spongy moss 

 and the bottoms are covered with a thick layer of decaying vegetable 

 matter which colors the water brown. Crustacea abound in all of 

 these, but fish and mollusks are absent from three and probably all 

 of them. 



On St. Paul Island there are a large number of lakes and ponds of a 

 different character. The bottoms of these are sandy or rock, and 

 the water of none has the brown tundra color. A few are brackish. 

 One is over three miles and another is nearly a mile long. The deep- 

 est is a little over 8 feet. This Pisidium has been found abundant in 

 four of these, which are known as Webster Lake, Ice House Lake, 

 Big Lake, and the small pool above and adjacent to Ice House Lake. 

 These are the only ones that have been carefully examined. 



In some of the deeper sections of these ponds the bottoms are cov- 

 ered with a dense green aquatic vegetation, and in shallower parts 

 grasses grow out and project above the water. The Pisidium do not 

 seem to burrow in the sand, but crawl about over it, and may be 

 found in abundance at the water's edge. Thus many are frozen solid 

 for seven months of the year, while others, living in the deeper sec- 

 tions, remain active throughout the winter and creep over the stems 

 of grasses and other submerged plants in arboreal, snail-like manner. 

 Large numbers have been collected through the ice, and this method 

 is recommended to malacologists throughout the north. 



Proceedings U. s. National Museum. Vol. 51 -No. 2160. 



475 



