230 Proceedings of Indiana Academy of Science 
(2) Wave action. Despite the lack of predatory enemies, mussels 
are uncommon on wave-swept beaches or elsewhere at two feet depth or 
less. Headlee and Simonton found numerous individuals thrown up on 
the beach following storms, and concluded that this is the manner in 
which their shoreward distribution is limited. The writer has seen 
very few such cases except those thrown up by human agency. Recently 
dead Anodontae sometimes float to the surface and are swept ashore, 
thus entitling them to the vernacular name of “floater.” 
The writer placed mussels experimentally in water of a few inches 
depth near the shore at various points about the lake. Sooner or later 
they were sure to turn and seek greater depths, oriented by a pressure 
sense. This movement is expedited in times of storm and high waves. 
The explanation is a matter of stimulation or annoyance by the moving 
water and sand in suspension. In protected areas the return to deep 
water is more leisurely. 
(3) Bottom. The above authors have very clearly shown how the 
several species are limited to the respective types of bottom in the lake. 
The matter of preference of certain types of bottom is a function of 
shell weight, at least in part. The Anodontae alone are found sometimes 
on muddy substrata, while the other species are sand dwellers, all having 
also moderate shell weight and erect posture. In the paper referred to 
in the introduction experiments along these lines will be described. 
During recent years no Margaritana marginata have been obtained 
from the lake. Almost no glans and fabalis have been seen. Rather 
few subrostratus and rubiginosa have been taken, and in both cases have 
been confined to small groups of individuals in a few localities. Swubro- 
stratus has been collected always in rather deep water off exposed points. 
Since so few localities of the favored type occur, we may thus account 
in part for their small numbers. 
The western shore is so inclined to the prevailing northwesterlies 
that southward shore currents are set up. (Fig. 1, arrows.) Thereby 
even the wind has a share in determining mussel distribution, locally. 
(Scott, 716, map opp. p. 14.) On every point of land this shore current 
picks up the mud from the northern margin and deposits it on the 
southern fringe of the same point, in the quieter water of the lee slope. 
Thus the beach has an alternation of sand and mud bottom on the west 
shore, arranged in serrate outline. The effect on mussel distribution 
may be seen with the help of the map (Fig. 1) and the table. A census 
of the two dominant species at various points demonstrates that not only 
general distribution, as shown by Headlee and Simonton, but also the 
minute local distribution is largely a matter of the character of the 
bottom. 
In the following table the records represent all the mussels found 
at a depth of from three to four feet, for a distance of a few rods, and 
on bottom areas selected at random. In all cases where sand is abundant 
luteolus predominated, and was nearly wanting on soft bottoms. Ano- 
donta oceurs often on sand, but oftener on mud or marly sand. Headlee 
and Simonton’s zones are thus shown not to correspond at all to contour 
lines, for the physiographic agencies which assort the bottom materials 
are complicated on the west shore by the action of the shore currents. 
