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, PI. 43, fig. 9, in outward 

 form is somewhat like our shell, but the figure, as with A. aquata, is not sufficient for 

 comparison, and the description is too concise to supply the deficiency. 



6. KELLIA COARCTATA, 8. Wood. Tab. XII, fig. 10, a, b. 



KELLTA COABCTATA. S. Wood. Catalogue, 1840. 



GALEOMMA COMPRESSUM? Phil. En. Moll. Sic., vol. ii, p. 19, t. 14, fig. 5, 1844. 



Spec. Char. Testa minutd transversd, oUongd, Itevigatd, politd, compressd, subcequi- 

 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, T T T ^ S - Height, Jth 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 onjy 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 striae, and the impressions of the muscles are not distinguishable. 



