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The sacrifice of a great number of these shells, large and small, in 

 search of the hinge, has been without success, excepting that, in one 

 specimen, I have ascertained the presence of a lateral tooth, beneath the 

 depression for the cartilage, on the truncated side. 



These shells are sometimes found of a prodigious size eight or nine 

 inches long, and as many in width. One before me, which I purchased 

 from the collection of the Marquis of Donegal, and which is, I believe, 

 from the neighbourhood of Bath, weighs, with the inclosed lime-stone, 

 nine pounds and a quarter. 



Here we must also place the thick fossil shell represented Plate XIII. 

 Fig. 7, which is also chiefly found in the counties just mentioned. This 

 specimen is interesting; as it shows, from the valves having slipped from 

 each other, the strong, boldly-projecting, lateral teeth, one of which is 

 to be seen on each side. I had the mortification of destroying many 

 good specimens, without gaining any further information respecting the 

 hinge of this shell. But after obtaining the specimen which is here 

 figured, I renewed my endeavours, and at last succeeded in separating 

 two valves : by which 1 ascertained the existence of two lateral teeth, 

 mutually entering, in each valve, and two thin cardinal teeth, converging, 

 tinder the beaks of one valve, between which a single tooth in the other 

 valve is inserted. 



Here I will also, for the present, dispose of the curious and anomalous 

 shell, Plate XI IT. Fig. 8. The imperfect, and perhaps delusive view, 

 in which this shell, the only specimen I have seen, is presented to my 

 view, makes me hesitate at the endeavour to point out its apparently 

 peculiar characters. It is a transvere inequilateral shell : the valves 

 thinly beset with transverse linear ribs; and at little nearer to the base 

 of the shell than the middle of the valve, on each side, is a flat ear-like 

 process, by the continuation from which the superior part of the valve 

 gains more than the eighth of an inch in width on each side. There 

 is not any tooth discoverable beneath the beak ; but the hinge appears 

 to have been formed, at least in one valve, by a groove formed in an 



