THE NAUTILUS. 15 



CN THE EROSION AND THICKNESS OF SHELLS OF THE FRESH-WATER 



MUSSELS. 



BY N. M. GRIER, PH. D., HOLLINS COLLEGE. 



In connection with another investigation, I had opportunity 

 to summarize what is apparently most of the literature dealing 

 with these little discussed and connected phases of the ecology 

 of the Naiades, and now wish to present it in the light of other 

 points this investigation brought out. 



Hey (1), compared shells of U. pictorum and U. tumidus from 

 the Ouse and Foss Rivers in England. The Ouse River is a 

 wide and deep stream with a great deal of mud and receives a 

 variety of drainage material. Hey believed the erosion of the 

 shells in it was due either to the dissolved C0 2 in the water, or 

 the rapidity of the current, for in the FOBS River, where condi- 

 tions were generally opposite ones, they showed little such dis- 

 figurement or none. Shrubsole (2) states erosion in shells may 

 be attributed to the low percentage of lime in the water, which 

 he analyzed, and found to be positively correlated with this 

 fact. Beauchamp (3), also, felt that erosion might be due to 

 dissolved carbon dioxide, for he found that shells were con- 

 siderably eroded in streams flowing through limestone forma- 

 tions; moreover dead shells in water containing an abundance 

 of lime were similarly affected. March (4), however, states 

 that shells from districts highly charged with C0 2 have thin 

 shells, which are not eroded at the beaks, and was inclined to 

 attribute this to the absence of humic acid, ' ' which does not 

 occur where limestone does; or the absence or excess of chalk." 

 Cooper (5) states that badly deformed shells are found in water 

 of excessive saltness, while Baker (6) noted in Cardium, a 

 marine pelecypod, that thinness of shell seemed correlated with 

 the saltness of the water. Finally, Rich (7) tells of some shells 

 ( Vnio complanatus*) from a soft-water lake in New York which 

 were almost free from lime. Further on in this paper it will 

 be shown that while the waters of Lake Erie contain more lime 

 than those of the Upper Ohio Drainage, shells are comparatively 

 thicker in the latter. 



It is at once observed that more of the above writers ascribe 



