BIVALVES — MYTILUS. 69 
MYTILUS. — Musc_e. 
DESCRIPTION OF PLATE XVI. 
Dw. I. —Fig. 2. M. pellucidus. Drv. VI. Fam. 2. Fig. 6. M. hirundo. 
Div. Il.—Fig. 5. M. discors. Dw. VIII. Fig. 3. M. lingua. 
Dw. IIl.—Fig, 1. M. lithophagus. Fig. 4. Interior of Fig. 5. 
Shell bivalve, rough, usually affixed by a byssus or beard of silky 
filaments ; hinge mostly without teeth, with generally a subulate 
excavated longitudinal line. 
OF the genus Mytilus forty-six species are enumerated ; 
though some of these are rather indistinct in character, 
yet the greatest proportion of them bear a near alliance 
to the general form and habits of the common or eatable 
Muscle. 
The hinge of the Mytilus is usually without teeth, 
having generally in their place a subulate excavated 
line. Some, however, have small denticulations, with 
alternate grooves, varying in different species from ten 
to fifty; in the M. niger, which has the greatest num- 
ber, they amount to nearly one hundred. 
A particular class possesses the faculty of penetrating 
coral and calcareous rocks; from which, like the Pholas, 
the shell cannot be extracted without breaking the sub- 
stance in which it is imbedded. Of this description are 
the M. lithophagus, M. rugosa, &c. the latter of which 
is sometimes found in lakes, as well as the sea. 
There are some species which are frequently mis-= 
taken as belonging to the genus Mya; such as the M. 
latus, M. discors, and M. angulatus; but, by a careful 
