Pvn H,i I'UitlS

140 ARCID.E.
Genus I. NU'CULA*, Lamarck. PL IV. f. 1.
Body roundish-oval, somewhat compressed : mantle open in
front and at both sides :
lapping
the other :
gills unequal in size, one pair over-
lips or palpi long and pendulous :
and having its margin serrated or notched.
foot oval
Shell triangular and compressed, highly nacreous : margin
of the posterior side rounded : lunule or area below the beaks
heart-shaped : ligament partly internal :
cartilage
contained in a : spoon-shaped cavity teeth sharp and recurved,
those on the anterior side being fewer than those on the other
side : pallial
scar entire.
internal and
The Nuculce inhabit mud, sand, and gravel in all the
marine zones on our coast ;
and they appear to be gre-
garious. They are found in every degree of longitude
and latitude throughout the globe. The umbonal area,
or that part of the shell which is terminated by the
beak, is often eroded and the nacreous layers exposed,
probably owing to the action of sulphuretted hydrogen,
which is evolved from animal matter in a state of de-
composition
contained in the mud. Sometimes the
beak is encrusted with a ferruginous or mineral deposit.
The lunule in the present genus and Leda projects considerably,
so as to resemble a pair of pouting lips. Each
organ (in the mollusk as well as in Woman) encloses a
row of dazzling white teeth. But here the analogy ends.
Such comparisons of natural beauty constitute one of
the minor charms of science, and may be pardoned in
an enthusiastic naturalist.
I am not prepared to accept D'Orbigny's proposition,
which has been adopted by Gray and other concho-
logists, that this genus ought to form a distinct family.
The genus Nuculana of Searles Wood resembles Nucula
in shape, but has teeth like those of Pectunciihts, and no
* A small nut.