MUSSELS. 
4:7 
to circumstances. It soon looses its regularity 
of form, and becomes oyster-shaped ; sometimes 
developing one valve and sometimes the other, 
as opportunity offers ; twisting itself to the right 
or left, and becoming so distorted that it seems 
to have wholly forgotten its youthful grace. In 
color, it varies from yellow to brown, on the out- 
side; while within, it is pure white, with a rich 
purple area at the hinge line. This purple color 
is very permanent, and fragments of shells may 
often be found, still showing it; the ligament is in- 
ternal, in a deep, narrow pit ; the muscular im- 
pression is smooth, and very large. This species 
sometimes grows to the size of a large oyster ; it 
is occasionally cast up alive from deep water, 
but dead shells are much more common. 
The last shell of this group which we shall 
mention is Lima orient alls, Ad. & Eve., File- 
shell, an inside view of which is shown in Fig. 
5, PI. XII. This little shell is pure white, and 
is thrown up from the sea attached to sea-weed. 
The valves are obliquely oval, thin, gaping, and 
sculptured like a file ; length, three-fourths of an 
inch. 
Mytilus edulis , Linn., is the common mussel, 
known to every one. Spinning its strong, horny 
byssus, it attaches itself to rocks, posts, and 
wharves, in countless numbers. Its smooth, dark 
purple shell and orange colored soft parts are 
too well known to need description. The com- 
mon length is two inches. 
Mytilus Calif or nianus, Conr., Fig. 6, PI. 
XII, is found covering the rocks over which the 
breakers dash the wildest. Moored by its strong 
