90 College of Forestry 
time on the ecrowfoot dredge. As observed in all stations 
studied, Hlliptio complanatus was the most abundant species. 
Three species were secured. 
Elliptio complanatus. Lampsilis borealis. 
Lampsilis radiata. 
B. ANALYSIS OF ENVIRONMENTS. 
A study of the forty-one stations described in the previous 
pages naturally leads to their division into several more or 
less distinct types. Each type is found wherever a given com- 
bination of environmental factors occur. These forty-one 
stations may be classified under four major heads, and thir- 
teen minor heads. It is not to be supposed that these habitats 
are sharply divided. On the contrary, they fade into each 
other more or less completely, the amount of gradation being 
governed by the sharpness of the characteristics of the inter- 
mediate zones. 
1. Laxr Types. 
I. Boulder-Bottom Type. (Figs. 11, 23.) 
Stations II, IV, XI, XIV, XV, XX and XXI are exam- 
ples of this type of habitat. The shore may be free from 
vegetation, or it may have associations of Water Willow 
(Dianthera americana) and Bulrush (Scirpus occidentalis or 
S. americanus). It receives the full force of the winds and 
waves from the open lake. The water is from 1 to 3 feet 
in depth and the bottom is heavily and thickly covered with 
stones and boulders, many of the latter being of large size. 
These shallow, rocky areas are almost always at the end of 
points of land which extend into the lake. Their area varies 
from 100 to 500 feet in length and from 50 to 200 feet in 
width. Animal life is abundant, the clams living between 
the stones and the snails on the stones and on the sand be- 
tween the stones. 
