THE NAUTILUS. S 
ON 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. pictorwm 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 
shellg in it was due either to the dissolved CO, in the water, or 
the rapidity of the current, for in the Foss 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 CO, 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 
( Unio 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 
