Pvn H,i I'UitlS

104 MYTILIM.
mined the beaks in a common mussel must see that
they are not placed at the end. Their comparative
distance from this point is in every case, whether of
Mytilus or Modiola, a mere question of degree. The
so-called Modiola are invariably fixed by a byssus ;
and
the typical species (M. modiolus) are attached to the beds
on which they congregate precisely in the same way as
Mytilus edulis. The only appreciable difference in a
generic point of view that I can detect between M. mo-
diolus and M. edulis is that in the latter the front
edges of the mantle are fringed, while in the former they
are plain, and also that the small tubercles of the hinge
in M. edulis only occur in the very young of M. modiolus,
and not in a subsequent stage of growth. In M. pha~
seolinus, however (which has always been regarded as a
Modiola), these tubercles are represented by minute
but distinct crenulations. The shells of all the British
species of Mytilus are smooth. The byssus proceeds
from a gristly shaft, which appears to support the bundle
of filaments like the handle of a broom. Mytilus is a
very ancient name, and was also spelt by classic authors
Mytulus, Mitulus, and Mutulus. The animal is the Cal-
litriche of Poli.
1. Mytilus edulis"^, Linne.
M. edulis, Linn. Syst. Nat. p. 1157 ; F. & H. ii. p. 170, pi. xlviii. f. 1-4,
and (animal) pi. Q. f. 5.
Body varying in colour from white to orange-yellow, with
a tint of reddish-brown or purple : mantle having two margins
; outer one plain ; the inner one pinnated, or fringed on
the ventral and anterior sides with 15-25 tentacular cirri, and
serrated on the branchial : portion foot dark brown, occasionally
streaked with wrhite down the middle.
Shell irregularly triangular, expanding from the smaller
* Eatable.