Pvn H,i I'UitlS

LIMOPSIS. 159
cial beck, but its habitation is now restricted to higher
latitudes. Both of these species belong to the genus
Leda.
Genus III. LIMOFSIS %
Sassi. PL IV. f. 3.
Body longitudinally oval, or inclining to a circular shape :
mantle open on all sides except the back : foot long, slender,
and pointed at each end.
Shell shaped like the body, nearly equal-sided, porcellanous
: epidermis hairy or fibrous : beaks incurved and diverg-
ing from each other in the course of growth :
cartilage thick,
contained in a shallow triangular cavity or depression, which
is placed directly under the beaks and outside the hinge-plate :
teeth tubercular, arranged in a continuous and curved line :
pallial
scar entire.
This remarkable, and what some would call
' '
critical,"
genus is related intrinsically to Leda, and extrinsically
to Pectunculus. Like the former, it has a cartilage,
with a cavity for its reception ; but this process is not
placed, as in Leda, inside the shell, but on the hingeline
and between the beaks and the hinge-plate. Pec-
tunculus has no cartilage ; and its shell is kept closed
behind by a ligament, which is wanting in Limopsis.
The teeth are arranged in a single continuous row, as in
Pectunculus, instead of in two separate
rows in the same
line, as in Leda, The shape of the teeth in the present
is intermediate between that of Leda and Pectun-
genus
culus, being
erect but blunt. The contour of the shell
is much more like that of the last-mentioned genus, but
it is somewhat longer in proportion to its breadth.
Limopsis has scarcely any
resemblance to Lima. Al-
though the back of the shell in both these genera is furnished
with a small wing or prolongation on the upper
part of each side, and the cartilage-pit is similar, Lima
* From its supposed resemblance to the genus Lima.