Pvn H,i I'UitlS

KELLIA. 223
metrical, and nearly triangular : lips two, of a similar shape :
foot long, tongue-shaped and bent, placed in the middle of the
front margin.
Shell globular : beaks incurved : cartilage cylindrical, placed
on the hinge-plate at the posterior side (being the broader and
larger end of the shell) : hinge containing
in the left valve a
thick, erect cardinal tooth, and in each valve two remarkably
strong laminar teeth which are partly cardinal and partly
lateral.
This genus diners from Lascea in the incurrent tube
being more complete and the excurrent tube conspicuous,
in the foot being placed in the middle of the
ventral margin (instead of on the anterior side and pro-
truding through a slit at the base of the larger tube),
but especially in the position of the cartilage, which
lies on the broader and larger side of the shell, sup-
porting the hinge-plate, and outside of the lateral teeth,
and not (as in the last genus) placed on the narrower
and smaller side of the shell, nor clasping the hingeplate
inside and below those teeth. The habits of the
are also different from those of Lascea.
present genus
This is not amphibious, and probably cannot exist if
constantly left high and dry by the receding
tide. It
usually inhabits comparatively deep water, and prefers a
muddy ground. Both are viviparous : but at least one
species of Montacuta has the same mode of reproduc-
tion. In the shape of its shell Kellia resembles Sphcerium;
but that genus has an external ligament and
differs from this in the number and arrangement of the
teeth. The position of the tubes is also very dissimilar
in these genera. In Kellia, as well as in Lasted, it is
somewhat anomalous, the larger and incurrent tube
being placed at one end, and the smaller and excurrent
tube at the other. In Sphmrium and most other genera
which have two tubes, both are placed on the same side ;