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lutrarise, crassatellas, & c. ; but a generic difference, in the opinion of 
Lamarck, exists in these shells : the cartilage is inserted in a pit 
between the hinge-teeth. He believes that the shells of this genus 
are only found fossil, and enumerates eleven species found in the 
environs of Paris : E. Icevis, E. pellucida, E. trigonia, E. incequilatera, 
E. fragilis, E. elliptica, E. undulata, E. pellucida, E. obscura, E. 
miliaria, and E. radiolata. Plate XIII. Fig. 13 and 14, are repre- 
sentations of the inner and outer sides of E. Icevis, copied from Lamarck. 
CXII. Petricola. A transverse inequilateral shell, gaping a little 
at both ends, and having two muscular impressions : two hinge-teeth 
on one valve, and a bifid one on the other. The cartilage external. 
Venus lithophaga, Linn, is given as a species of this genus, which 
has not been described in a fossil state. 
CXIII. Umax. An equivalved inequilateral bivalve : the fore side 
the bluntest. The hinge-teeth two, either in one or both valves : the 
lateral teeth one or two, rather distant. 
The shells of this genus are strongly characterized by their nearly 
triangular figure, derived chiefly from the obtuse, and, as it were, 
truncated form of the fore side. When they have two lateral teeth, 
they are situated one on each side, with the hinge-teeth between 
them. The hinge-teeth themselves are sometimes two on each valve, 
and sometimes there are two on one valve, and but one on the other. 
Lamarck describes the following species as having been found in 
the neighbourhood of Paris : D. retusa , I), incompleta, JD. tellinella , 
D. nitida, D. lunulata, and D. obliqua. 
Plate XIII. Fig. 6, is a very small specimen of a fossil -shell which 
is very frequently found in Gloucestershire and Somersetshire, near 
to Bath. I have introduced it in this place, not knowing one more 
appropriate, and trusting that its form may excuse a temporary 
disposal of it here, until a more satisfactory examination may detect 
its real characters; which, I think, will be found different from those 
of any known recent shell 
