BIVALVIA. 49 
Shell small, ovate, equilateral, tumid, and closed, costated, central portion with 
7-9 angulated ribs, becoming obsolete or disappearing on the sides; hinge margin 
straight, with a trigonal and concave pit for the cartilage. 
Height, 3;. Length, 3,. Depth of united Valves, 1; of an inch. 
Locality. Cor. Crag, Sutton. 
This pretty little shell is very abundant in the Coralline Crag, at the above 
locality. 
It appears to be quite distinct from the preceding, and differs in several 
characters, and there is no species recent or fossil known to me to which it can be 
assigned. 
It has about seven angularly formed coste, which occupy the central portion 
of the dorsal area, beyond these are faint traces of striz, and in well preserved 
specimens the shell is semi-transparent, rendering these ribs visible in the interior, and 
giving about half a dozen rough crenulations to the ventral margin of the shell. 
The ligamental area is large, and the central pit diverges from the umbo under an 
angle of about 80°, muscular impression subcentral and ovate. It differs from any of 
the specimens of the preceding species of the same size, in being thicker and more 
regularly ovate, the ventral margin is more pointed, the sides are less straight, 
while the coste are more prominent and distinct. I have not seen JL. sulculus, 
Leach and Lovén, but the descriptions do not accord with our Crag shell, as it wants 
the “mediis binis verticalibus,” mentioned by the latter author, but which character 
may be seen in specimens of L. subauriculata. 
PInNA.* Jinneus. 
Pinna. Arist. Aldrov. List. Linn. Lam., Sc. 
Prennarta. Browne, 1756. 
Cuprera et CoHim#RopERMA. Poli., 1795. 
Perna. Adans, 1757. 
Oxysma? Rafinesque, 1819. 
CuRVULA. Id. 
Arrtna. Gray, 1840. 
Generic Character. Shell equivalved, mequilateral, oblique, triangular or wedge- 
shaped, generally thin and fragile; umbones terminal, hinge rectilinear, without teeth ; 
anterior margin sinuated and slightly gaping for the passage of a byssus; posterior 
truncated. Impression by the mantle entire; ligament internal. 
Animal triangular, in conformity with the shape of the shell; its mantle open or 
disconnected on all sides, except the dorsal edge, while its lobes line the whole 
interior of the valves; the lobes are ornamented with a double row of tentacular 
* Etym. révva, Arist., a kind of Pearl Oyster. 
