170 



ficient Id sinotlier it. That there is an oveiiyiiiji' sediment is shown 

 by the following- experiment: We pumped w;iter from twelve and six 

 inches above the sandy and gravelly bottom in seven, ten. tifteen, 

 twenty-five feet of water; the specimens revealed no sediment that 

 wotild not settle on standinji'. Specimens were taken in thirt.v and 

 thirty-six feet of water over a marl bottom and the twelve-inch samples 

 yielded a small amount of such sediment, while the six-inch samples 

 showed a decided amount. Tliat matter in suspension is fatal to the 

 mussel is shown by the fact that we found in the west side and south 

 end of the lake what were evidently once thriving mtissel l)eds, Iniried 

 under a thin layer of coarse marl, which had Ijeen stirred tip by the 

 action of the steam dredge two years l)efore. These mussels were 

 found in the normal position undisturlied in any way. That the mussels 

 were alive five years ago is shown l)y I>r. Moenkhaus" statement that 

 he and his classes collected an ahundance for study in those same regions 

 at that time. 



In order to test the abilit.v of the mussel to stand these bottom 

 conditions we made three wire clam l)askets. lowered one in twenty- 

 five feet of water, another in thirty-five feet, another in eighty-five 

 feet. "We got the following results: 



August •"). a basket containing thirteen T'. luteolus and one A. grandis 

 was placed in I'o feet of water on a dark marl bottom. On the loth 

 two examples of T'. luteolus were dead: on the l.'th one U. hiteohis was 

 dead-; on the 17th two U. luteolus were dead and four were missing. 



August '.). a liasket containing five T'. luteolus of the light variety 

 and one of the dark, and one A. edentula was lowered in 35 feet of water 

 on a sandy gi-ay marl iiottom. On the l.'itli, one A. grandis and one U. 

 rtibiginosus were added. On the 2(ith (lue I', luteolus of dark variety 

 was dead: on the 24tli five U. luteolus and ctue V. rubiginosus were found 

 to have the gills liadly choked witli si diment. while the anolontas were 

 missing. 



Angiist 1.1, a basket containing seven T'. luteolus of light and one of 

 dark variety, two -A. edentula. and one A. grandis was lowered in 85 

 feet on a pure dark marl bottom. On the 21st one U. luteolus of dark 

 variety was dead: on the 24th seven I', luteolus and one A. grandis 

 phowed gills liadly choked A\'itli sediment, while the two edentida were in 

 better conditi()n, showing very few patches of marl in gills. 



