428 MARINE INVERTEBRATES 
Mytilus edulis is exceedingly abundant along the New England 
coast. It lives in colonies, often between tides, in pebbly stations 
among large rocks. It is always 
so fastened by its byssus that the 
beaks of the valves point down- 
ward, and the ventral margin pro- 
jects above the sand or mud. 
The color of the epidermis in the 
adult form is black or a deep blue- 
black; the shell proper is violet. 
Hinge-teeth are wanting. Length 
two and a half inches. A variety 
of this species, M. pellucidus, 
is often found associated with the typical form. Itis brightly rayed in 
green.and yellow. M. edulis occurs in Europe, where it is quite exten- 
sively used as food. It also occurs (by importation) in San Francisco 
Bay. 
M. hamatus has a more southern range than has M. edulis, and is 
found from the Chesapeake southward. Its shell is considerably twisted 
just below the umbonal region, while its whole surface is densely striated. 
Its color is dark fuscous. Length one to two inches. It is found in 
great numbers attached to oysters by its byssus. In Florida it is very 
common. (Plate LXXVIII.) 
M. californicus. A common west-coast species, which finds its sta- 
tion among rocks exposed to the surf. It is about the same size as M. 
edulis, but has a lighter brownish glossy epidermis and several con- 
spicuous, well-rounded, radiating ribs. The animal is orange-colored. 
Modiola modiolus. After violent storms upon the New England 
coast, when a large Laminaria is wrenched from its rocky bed and 
washed ashore, its roots will, in many cases, be found clinging to this 
large mussel. The thick glossy epidermis of deep chestnut-color folds 
over the margin of the valves, and the outer surface, especially near the 
ventral margin, is covered with a tough hairy growth. Length four to 
five inches. The animal is orange-red. The great size and swelling full- 
ness of this species at once distinguish it from all others upon our coast. 
It is not a shallow-water form, 
but is extremely common upon 
all beaches north of Hatteras. 
It also occurs in Alaskan 
waters to Puget 
Sound, where it 
is known as the 
“oreat horse- 
mussel.” Some- 
times these large 
modiolas may be 
found in rocky 
tide-pools which 
are washed by the surf at high 
tide. They hide far back in 
the crevices of boulders, and Modiola modiotus, 
Mytilus edulis, rayed-color variety. 
