Pvn H,i I'UitlS

MODIOLARIA. 129
brown or even pitch-black in aged examples : margins rounded
on all sides except the ventral, which is nearely straight :
beaks small, prominent, incurved, and diverging, placed at
some distance from the anterior margin : byssal sinus, ligament,
and hinge-line as in the other species : hinge-plate strength-
ened by a rib to receive the ligament, and hnely notched;
ligamental groove narrow and deep : hinge
crenulated : inside
highly nacreous, purplish-brown, finely notched on the anterior
and posterior edges, and showing the impressions of the
ribs as well as faint traces of similar but finer striae on the
middle area : scars distinct. L. 1*5. B. 0*65.
Habitat :
Muddy gravel, at depths varying from 7
to 90 fathoms on the coasts of Yorkshire, Northumber-
land, and Durham, both sides of Scotland, and the Shetland
Isles. Although not generally distributed, it is not
uncommon in some places, and in the Firth of Forth it is
called by the fishermen the " corduroy mussel." The
Dogger bank appears to be its southernmost limit in our
seas. The Rev. H. W. Crosskey found a single valve in a
and Mobius
postglacial bed in the Kyles of Bute. Meyer
obtained specimens by dredging in the bay of Kiel, on
the German coast of the Baltic, whence the species
ranges northwards along the Scandinavian shores to
Nova Zembla on the east, and Iceland on the west. On
the other side of the Atlantic it inhabits the coasts of
Greenland, Newfoundland, New England, and Massa-
chusetts.
This fine species may be at once known from M.
discors by its sculpture. There are nearly twice as
many ribs on the posterior area, and the transverse stride
or wrinkles are so coarse as to give a granular appear-
ance to that part of the shell. Besides,
margin is more produced, and consequently
the anterior
the beaks
recede further from that extremity. The fry are quite
smooth and have a prismatic lustre. The largest specimens
I have seen were lately procured on the Durham
g 5