634 JAMES L. KELLOGG 
The progress of material along the proximal part of the oral 
groove and its disappearance into the mouth, is not easy to fol- 
low, for reasons that will appear; but it has been seen clearly in 
Schizotherus, Mytilus, Mytilimeria, Pecten, and other forms. 
The removal of material not used for food 
An observation of waters in which lamellibranchs live, whether 
of lakes, rivers, or seacoasts, will reveal, through the seasons, 
many great changes in conditions, such as variations in temper- 
ature, salinity, or food supply, and there is still much to be 
learned of the effects of such changes on these forms. There is 
one condition, however, the effect of which on lamellibranchs 
can now be described in detail—the periodical loading of waters 
with mud or fine sand which occurs everywhere as an effect of 
rains, tide currents, or wave action. No waters are clear all 
the time, and most of them, even on rocky seashores, sometimes 
bear very large quantities of sediment for comparatively long 
periods. 
Without doubt, sediment-laden waters present a serious prob- 
lem to lamellibranchs, which feed on floating organisms, and if 
the cilia tracts, above referred to, were the only ones in opera- 
tion, mud or sand, as well as diatoms, would of necessity be 
carried into the digestive tract as long as the valves of the shell 
remained open. I have found that species of the genus Macoma, 
of the Pacific coast, habitually take beach sand into the diges- 
tive tract until it is distended from stomach to anus, but I have 
observed no other cases of the sort. It is true that sand grains 
in relatively small quantities are usually found in the stomachs 
of lamellibranchs; but it appears to be perfectly certain that 
generally the ingestion of quantities of material, other than 
diatoms, is injurious, and is avoided as much as possible. But 
to close the shell to prevent the entrance of water for long periods, 
would interfere with respiration. While some lamellibranchs are 
able to survive for days, or even weeks, in cold weather, when 
removed from the water, experience with oysters and clams 
show that adult individuals, at least, are injured by the treat- 
