326 2 Variation in Shells. [ ZOE 
however, it attains its greatest size as well as number. I have 
found it as far south as Los Angeles, but it cannot .be said to be an 
abundant shell south of the Oregon line —at least I have not found 
itso. In the ponds and lakes of Washington, however, it is quite 
plentiful and leads an active life, as it can be traced by the deep 
furrows it plows through the soft mud and sediment in seeking its 
food and companions, or moves on, perhaps, by mere force of habit. 
One other species, Anodonta angulata Lea. (figs. 5 and 6), is 
- decidedly a river mussel, and is as rarely found in ponds or lakes 
as A. Oregonensis is found in swift-running streams. Some years 
ago I found two specimens of this shell on the shores of Blue Lakes, 
Lake County, California, and the only ones I have found of this 
species in ponds or lakes. It is somewhat gregarious in its habits, 
and from its position when burrowing in the sand and mud I am 
strongly impressed with the thought that it seldom leaves its situa- 
tion in swift-running streams, unless compelled by force of adverse 
circumstances. 
About twelve or fifteen years ago I found a colony of A. angudata 
in the San Joaquin River, California, by wading out into the stream 
to where the water was waist deep. This colony had located itself 
in a bed of stiff clay on the edge of a steep bank that led into the 
channel of the river. By working my feet into this clay I could feel 
the edges of the valves, and then, reaching down, dig them out with 
my hands. The depth and muddy state of the water prevented me 
from making observations on their habits further than noting that — 
they were gregarious, as I found them burrowing in close proxim- 
ity to one another in the stiff clay, with the anterior end of the shell 
up. 
In the fall of 1889, after rather a hard summer’s trip through the | 
northern mountains collecting shells, I reached Weiser City, on the © 
banks of the small river bearing the same name, at its junction with 
Snake River in Idaho, early in the month of October. The sum. 
mer and fall had been excessively dry, and many of the springs and _ 
small streams in that section of the country had dried up and Snake 
_ River had fallen almost to the proportions of a creek, exposing many 
_ of the low bars and portions of the river’s bed that had not been 
uncovered for years. This low stage of the water offered a good 
opportunity for taking notes and making observations on the habits 
of this class of fresh-water shells, which very fortunately I found 
_ abundant. 
