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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 in- 
formation 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 I ascertained the 
existence of two lateral teeth, mutually entering, in each valve, and 
two thin cardinal teeth, converging, under 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 andanomalous 
shell, Plate XIII. 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 transverse 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 
