MUSSELS OF WINONA, PIKE, AND CENTER LAKES. 315 



into the bottom enough to give them soil in which to right 

 themselves. 



We placed three specimens of each species experimented upon, 

 except U. rubiginosiis, in a tub, which had previously been two- 

 thirds filled with fine dark mud from the deep area, and then filled 

 up with water. This water was freshened by the use of Elodea 

 and the occasional addition of clean water, which was so added as 

 not to disturb the mud. After seventeen days all of U. lutcolus, 

 two of U. subrostratus, and one of A. grandis showed mud in 

 gills, thus effectually demonstrating that the basket was not alone 

 to blame for the general failure to withstand the fine black mud 

 of the bottom. 



The work of 1903 and 1904 shows conclusively that the 

 mussels of Winona, Pike, and Center lakes cannot exist on the 

 fine black mud bottom they become choked with mud and 

 apparently smother and that the light weight forms and 

 the forms exposing great surface in proportion to weight can rest 

 on top of comparatively soft mud and can, therefore, live farthest 

 out on the deep water edge of the bed. Because the mussels 

 cannot occupy any region where the pure black mud is present, 

 they are confined by it to isolated beds and narrow bands of 

 shore-line. 



I believe that the whole evidence of the distributional and ex- 

 perimental work of 1903 and 1904 points clearly to the charac- 

 ter of the bottom as the great basal influence in the distribution 

 of mussels in small lakes generally. 



ADDITIONS TO THE KNOWN FAUNA. 



We knew that various species of Splicei'iiim had been taken 

 in Turkey and Maxinkuckee lakes and therefore hoped to find 

 more than the one thus far reported from Winona. 



Mr. A. M. Banta told us of a small bivalve that he had dis- 

 covered in an artificial lily-pond in the assembly grounds near 

 the lake. It required but little effort to find it in the decaying 

 vegetable matter in the bottom of this pond, but we did not take 

 it in the lake. It is Sphcsrium partumeium Say. It has not been 

 reported from this region before. The dead shells of Splice- 

 rinm striatinuni Lamarck occur in great numbers along the 



