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, where the edge of the smaller valves rests against the 

 inside of the elongated cylindric part of the larger valve, generally 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 

 suspectjng 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 sup- 

 posed. In a bivalve, we have one cavity for the habitation of the ani- 

 mal ; 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, c. 



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 b. 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 b 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, I may have made some mistake, 

 which those who possess more illustrative specimens may be able to 

 correct. 



