140 MOLLUSCA FROM THE CRAG. 
Diameter, 1Zths of an inch. 
Locality. Cor. Crag, Sutton, Ramsholt, Sudbourn, and Gedgrave. 
Red Crag, Passim. 
Mam. Crag, Postwick and Thorpe. 
Recent, Mediterranean, Britain, Scandinavia, and North America. 
This is one of our most abundant shells in the Coralline as well as in the 
Red Crag. 
In the young state, it is rather less equilateral than in the adult, and has 
comparatively a larger and deeper lunule, with the teeth more distinct and prominent. 
It is nearly orbicular, though sometimes there is a trifling difference in the dimensions, 
the diameter from the anterior to the posterior side exceeding that from the umbo to 
the ventral margin, and vice versd. In the right valve are two cardinal teeth, one 
large and bifid, the other small and simple, with a prominent lateral tooth on the 
anterior side, and in the left are also two cardinal teeth, one simple and the other 
bifid, but their positions are reversed, the bifid one in the left being the anterior, with 
a corresponding lateral tooth on that side. The interior is often strongly marked with 
radiating strize, most distinct beyond the edge of the mantle mark : there are two deep 
impressions by the adductor muscles, the posterior of an ovate form, the anterior one is 
much elongated, being as it were bipartite, that nearest the anterior lateral tooth of 
the usual form, with a ligulate prolongation down to near the middle of the shell; in 
addition to which, in the interior about the centre is a banded impression extending 
half way across the shell, in a direction at right angles to the ligamental fulcrum, as 
if the mantle had there a division. In some specimens, the exterior is covered with 
close-set laméllated strize, and the shell is somewhat tumid, while in others the shell is 
flat or much compressed, and the concentric markings distant. A little inflection is 
always to be seen on the posterior side, producing a more or less distinctly marked 
sinus, and both sides are generally a little elevated, giving the shell the appearance of 
being high-shouldered. A small but distinct lunule is visible, curving strongly near 
the umbo, which gives to the young shell a comparatively larger mark there than 
when it is full grown. This shell is said in the recent state to have a range from 
low water-mark to the depth of 90 fathoms. 
2. LucINA CRENULATA, S. Wood. Tab. XII, fig. 7 a, 6. 
Luctna crenuLata. 8S. Wood. Catalogue, 1840. ; 
—  srriaTuLa? Nyst. Rech. Coq. Foss. de Hoesselt et Kl. Sp., p. 5, No. 11, pl. 1, 
fig. 11, 1836. 
— — 2? WNyst. Coq. Foss. Belg., p. 131, pl. 6, fig. 9, a—e, 1844. 
— oentata? Goldf. Pet. Germ., vol. ii, p. 230, t. 147, fig. 1. 
—  crenuLAtTA. Conrad. Amer. Mioc. Foss., p. 39, pl. 29, fig. 2. 
Spee. Char. Testd parva orbiculari, equilaterali, convexd, concentricé striatd, striis 
numerosis confertis, lunuld impressd, elongato-ovatd ; dentibus lateralibus distinctis ; margine 
crenulatd. 
