Pvn H,i I'UitlS

LIMA. 83
Shell oblong, extremely convex, rather thin and glossy,
semitransparent : sculpture, 24 slight but sharp ribs, which
radiate from the beaks and do not extend to the sides ; the
middle rib is the largest, and runs straight down to the front
the ribs are crossed by extremely fine and numerous
margin ;
concentric stria?, making the crests appear somewhat : jagged
colour milk-white: margins rounded in front, and sloping with
a gentle curve upwards to the ears: beaks extremely prominent
and gibbous, projecting considerably beyond the : hinge
ears triangular, very small, hanging a little downwards : carti-
lage diamond-shaped, occupying nearly one-third of the hinge :
in the
ligament narrow and slight : hinge-line straight except
middle, where it is incurved : hinge-plate sharp : cartilage-pit
forming an acute triangle, faintly striate across under ; each
ear is a shelving triangular space as in L. ellipjtica, but pro-
narrower : inside
portionally
highly nacreous, and marked by
a furrow which runs down the middle, and is the reverse or
under side of the central rib ; it is also indistinctly grooved
by the impression of the outside ribs ; front margin slightly
notched by the edges of those ribs: muscular scar faint.
L. 0-275. B. 0-15.
Habitat :
Sandy
and gravelly ground in almost every
part of the British seas, from 18 to 90 fathoms. It is
also a Coralline Crag fossil. Its distribution in other
parts of the northern hemisphere is very extensive, em-
bracing Greenland, Iceland, Scandinavia, the Adriatic,
both shores of the Mediterranean, the iEgean, and the
Canary Isles. Nor is its bathymetrical range in widely
separated seas less worthy of remark. Wallich obtained
it by means of his deep-sea soundings in the North
Atlantic from 227 fathoms ;
and M'Andrew has recorded
the depths at which he dredged living specimens on the
coast of upper Norway as 15-150 fathoms, and Forbes
in the iEgean as 15-140 fathoms.
The animal is shy. It uses its foot for crawling. The
alimentarv and branchial current enters in at the middle
of the front margin ; and the excretory current passes
out below the ear on the posterior side. In a single