Pvn H,i I'UitlS

154 ARCID.E.
writers to the so-called genus Yoldia, is closed at both
ends. These (and probably L. pernula) being the only
species indigenous to our seas, I must hesitate before
admitting the proposed division of Leda into two genera,
so far as concerns the British Mollusca.
A. Shell triangularly oval, smooth and polished; posterior
extremity rounded and closed : lunide indistinct ; teeth set
like those of a comb.
1. Leda pygm^e'a*, Minister.
Niccula pygmcBa, (Minister) Goldfusa, Petref. p. 157, t. cxxv. f. 17. L.
pygm&a, F. & H. ii. p. 230, pi. xlvii. f. 10, and (animal) pi. P. f. 3.
Body pale fawn-white colour : tubes short, united, with plain
orihces : foot hatchet-shaped, and widely grooved at its posterior
edge, forming when expanded a crenated disk.
Shell nearly equilateral, sloping gradually from the beak to
each side, tumid, glossy, and iridescent : sculpture, only a few
irregular marks of growth :
colour pearl-white under the epi-
and lustrous :
dermis, which is yellowish -brown, highly polished
margins rounded at the anterior side, with an oblique slope to
the ventral range, which is also rounded, somewhat produced
and wedge-shaped at the posterior side, with a slight tendency
to curve upwards :
recurved ;
beaks small and blunt, rather incurved than
lunide lance-shaped, but scarcely visible, and faintly
denned by an obscure ridge, which runs from the beak to the
posterior angle in each valve : ligament exceedingly slight :
cartilage and the cavity containing it very
Jiinge-line slightly curved, occupying nearly
small and short :
the whole of the
dorsal area and considerably more than one-third of the circumference
: hinge-plate deeply grooved, and becoming wider
as the distance from the cartilage-pit increases : teeth rather
long and sharp, placed on the inner margin of the hingeplate,
slightly curved outwards or reflected ; there are 10-12
on the anterior side, and 12-14 on the other : inside glossy,
with the margin somewhat thickened and entire : pallia! and
muscular scars slight, except in aged or dead specimens.
L. 0-15. B. 0-2.
* Dwarf.