BIVALVIA. 123 
Two or three specimens only of this delicate and fragile shell were all that I 
possessed when Mr. Sowerby figured and described it in ‘ Min. Conch.,’ and I am sorry 
to say I have seen none in addition to that number. A recent shell from the 
Mediterranean above referred to, seems to correspond in most characters with our 
own, and I should imagine there was no doubt of the identity, but that the Crag shell 
is wholly destitute of lateral teeth, which M. Philippi describes as being distinct in 
his species. The hinge was probably furnished with one cardinal tooth in the right 
valve and two in the left, but in my specimens of both valves they are nearly obsolete. 
The recent shell was no doubt in a better state of preservation and more to be de- 
pended upon. 
Its outward form and absence of all flexuosity in the margin will distinguish this 
from the preceding, which probably it resembled in its dentition. In the general 
form and fragile texture it much resembles one of the Freshwater Cyclades, whence its 
specific name. 
Amphidesma equalis, Conrad, ‘ Amer. Mioc. Foss.,’ p. 76, Pl. 43, fig. 9, in outward 
form is somewhat like our shell, but the figure, as with 4. equata, is not sufficient for 
comparison, and the description is too concise to supply the deficiency. 
6. Kexxira coarcrata, S. Wood. Tab. XII, fig. 10, a, 4. 
Kettra coarctata. SS. Wood. Catalogue, 1840. 
GALEOMMA compressum? Pil. En. Moll. Sic., vol. ii, p. 19, t. 14, fig. 5, 1844. 
Spec. Char. Testa minutdé transversd, oblonga, levigatd, politd, compressa, subequi- 
laterali ; antice majiore, dente cardinali unico in utraque valvd, lateralibus nullis ; margine 
ventrali recto, vel coarctato. 
Shell small, transverse, oblong, smooth, and glossy, compressed nearly equilateral, 
anterior side the larger; hinge with one cardinal tooth in each valve, lateral teeth 
none, ventral margin straight, or subsinuated. 
Length, ~ ds. Height, 4th of an inch. 
Locality. Coralline Crag, Sutton. 
Two or three dozen specimens of this species are in my Cabinet, all from one 
locality. The form of the shell is somewhat oblong, rounded at the corners; 
the posterior side is not only the shorter, but is rather narrower; the dorsal margin of 
the anterior side being nearly straight, while the posterior has a gentle slope by which 
that side is a little diminished. The exterior in perfect specimens has a beautiful 
glossy appearance, and it was probably in the living state a semitransparent shell. 
There is one tooth in each valve, that in the right is the larger and more prominent, 
behind this is the ligament, placed on an oblong kind of shelf, inclining inwards on the 
posterior side, the edge of this shelf is in some individuals slightly elevated above the 
margin, and might be mistaken for another tooth; the lines of growth are occasionally 
visible but no regular striz, and the impressions of the muscles are not distinguishable. 
