SHELLS OF LAKES AND STREAMS 305 



THE SPHERE AND PEA SHELLS 



In springs, lakes, and streams having a mud bot- 

 tom are found small shells distantly related to the 

 Cardiums of the ocean. They are curious little fel- 

 lows and have interesting habits and peculiarities of 

 distribution. 



One of the largest on the Pacific Slope is 

 Sphd:riu??i dentatum^ Haldeman, the Harrowed 

 Sphere-shell, Plate II, Fig. 5. It is moderately in- 

 flated, oblong-elliptical, with low umbos set some- 

 what forward. The shell is covered with low 

 growth ridges. It lives in lakes and streams in the 

 Columbia, Klamath, and Nevada Systems. 



Muscullum resembles Sph(^rium but the shells are 

 thin, light colored, and usually have a little cap or 

 calycule on each umbo. 



One June day, while on a collecting trip near Te- 

 hama, in northern California, I called to my friend, 

 an odd little German, to stop as we came to a large 

 pool at the roadside. Unhooking my net, I jumped 

 off my wheel to collect a few shells. The net con- 

 sisted of a heavy wire ring about six inches across 

 with a piece of burlap sewed into it forming a shal- 

 low bag. A smaller loop of the wire an inch or two 

 across served to hold it by, and made it convenient 

 to carry on the handle-bars of my wheel. Scooping 

 the net full of muci, I shook it carefully under the 

 water, picking sticks, leaves, and gravel out by hand 

 while the mud washed through, leaving only fine 



