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and concave, clasped or surrounded by the larger valve, and longi- 
tudinally and sometimes transversely striated. 
Its most striking characteristic is, the lengthened cylindric form of 
the convex valve. This is always filled with lime-stone, which entirely 
conceals from observation the other part of the shell, as long as the spe- 
cimen remains whole. With the slightest blow of a hammer, however, 
it constantly divides, ivhere the edge of the smaller valves rests against 
the inside of the elongated cylindric part of the larger valve, gene- 
rally about half an inch or less from the top of the shell ; Fig. 9, a, one 
side of the valve, before hidden, then becomes visible, as at Fig. 10. 
Thus far is the description of Mr. Martin ; but I must here add, that 
my late worthy friend, Dr. Menish, was strongly of opinion that this 
was not the whole history of the shell, and that there were reasons for 
suspecting that this shell was a multivalve. I am not in possession of the 
particular specimen on which the Doctor rested chiefly the support of 
his opinion. I will avail myself, however, of the specimen before us, 
to show that the structure of this shell is not such as has been hitherto 
supposed. In a bivalve, we have one cavity for the habitation of the 
animal ; but, in this specimen, there appears to be at least two : one 
between the upper valve, Fig. 9, and the lower valve, Fig. 10 ; and 
another above, which is shown by the fracture at Fig. 9, e. 
I am aware that it may be contended, that I may have been led into 
a mistake by the lower valve having split ; and that the upper half 
remains attached to the bottom of the upper valve at a, Fig. 9, whilst 
the lower half adheres to the mass Fig. 10, at h. But I cannot 
readily admit this to be the case here ; since, at a, the incumbent 
beak of the upper valve is plainly to be seen, and at h is the little pit 
in the lower valve for its reception, both of which could not be seen 
if the valve had split. It may also be said, that the upper valve might 
be naturally hollow ; but, even if this circumstance be admitted, that 
will, I hope, be allowed to be an anomaly, worthy of being thus 
shown. Possessing only this specimen of fellow valves of this shell, 
