177 



To sum up: In the basket in twenty-five feet, lowered on dark marl, 

 in nineteen days five Avere found dead and four missing; in tlie basket 

 in tlilrty-five feet, lowered near Sandy Point on a sandy gray marl l»ottom. 

 in fifteen days one was dead, all sliowed gills partly filled with si>diment: 

 in tlip 1)asket in eiglity-five feet, lowered on pure dark marl, in nine 

 days two were found dead and the gills of all but A. edentula badly 

 choked witli sediment. U. faltalis. U. glans and U. subrosti'atus were not 

 included in tliis experiment 1)ecause the first two would liave slipped out 

 through tlie meshes and the third could not be obtained at the time. 

 However, it seems reasonable to suppose that they would have proven 

 not unlike the others. It seems, therefore, that tho.se forms possessing" 

 light weiglit in proportion to surface exposed and close-fitting valves 

 are best able to I'esist the soft marl and the overlying sediment. 



A. grandis and edentula. having light and close-fitting valves, are 

 found accordingly on the outer edge of the sandy marl l)ank; the edentula, 

 being better fitted to withstand the liottom conditions, is found out 

 in the edge of the dark marl. U. glans and fabalis. owing to lightness and 

 close-fitting valves, occupy about the same situation, the fabalis having 

 much tlie lighter shell, tieing found out as far or farther than the 

 edentula. They are also found insliore. where not sulijected to wave 

 action. I', subrostratus. liaving medium weight valves, which are also 

 close-fitting, is confined to the gravel and sand banks, weed patches and 

 chara-covered beds. U. rubiginosis, having very heavy and rather loose- 

 fitting valves, is confined to clear sand and gravel banks. The dark 

 form of luteolus. liaving extremely heavy and rather loose-fitting valves, 

 is confined to hard sand and gravel banks. The straw-colored form by 

 its medium weight and tight-fitting valves is able to live on sand, gravel, 

 in mud i)atches and on chara-covered bottoms. Owing to the fact that so 

 few specimens of :\I. marginata were found we were unable to draw any 

 conclusions as to its ecology. 



The muskrat is the principal enemy of the mussels; around his 

 house many mussel sliells are found, but no live mussels. Shells of 

 all the species in the Lake except tlie smaller ones are found, the Ano- 

 donta shells being in much greater evidence than is proportionate to 

 their total nunilier. They do not appear so on first examination, for 

 they are Ijroken up by the animal and worn by the waves. The con- 

 ditions on the sand l)anks beyond reach of wave action are very favor- 



12— A. OF Science. '03. 



