128 MOLLUSCA FROM THE CRAG. 
Shell very inequilateral, subrhomboidal or slightly wedge-shaped, compressed 
or flattened, covered with concentric striz; posterior side very short, angulated, 
anterior produced, slightly contracted, and rounded ; ventral and dorsal margins nearly 
straight ; two diverging teeth in each valve, much the larger in the right; a small 
triangular ligamental cavity placed immediately beneath the umbo. 
Length, 3ths. Height, + of an inch. 
Locality. Cor. Crag, Sutton. 
This species is by no means scarce at Sutton, although valves of the above 
dimensions are not very often met with. 
There are differences in this shell that seem to justify a removal from the pre- 
ceding, although it must be confessed it is very nearly related, and in the immature 
state it is exceedingly difficult, if not impossible, to separate them, but what are con- 
sidered to be the distinctive characters may be pointed out leaving to future obser- 
vation to confirm or refute their identity. 
In the recent species (4¢dentata), the shell is not only less in size but more 
tumid, and nearly smooth, our fossil is compressed, and the body of the 
shell much flattened, the posterior side is particularly short and truncate, sloping 
direct fromthe umbo. On the anterior side, which constitutes nine tenths of the shell, 
the dorsal and ventral margins are nearly straight but not quite parallel, the termi- 
nation rounded and narrower, giving a somewhat cuneiform shape to the shell; the 
exterior is covered with regular and large concentric striz or lines of growth, and the 
ventral portion of the shell is slightly compressed, with an imperfect angular ridge on the 
shorter side: the right valve has two large diverging teeth, the posterior one being 
the smaller ; between these and immediately beneath the umbo is a small triangular 
cavity for the ligament. In the left valve, the margin is elevated into angular 
denticles which are inserted, when the valves are closed, between the margin and the 
teeth of the opposite valve. Muscular impressions not very distinct. 
3. Montacura susBstriata, Montague. Tab. XII, fig. 12, a, 6. 
LicuLa supsTRrata. Mont. Test. Brit. Sup., p. 25, 1808. 
Mya supstrrata. Dillw. Desc. Cat. Rec. Shells, p. 47, 1817. 
— — Turt. Conch. Dict., p. 103, 1819. 
— -- W. Wood. Ind. Test., p. 11, No. 22, 1825. 
Monracuta supstriava. Turt. Brit. Biv., p. 59, t. 11, figs. 9, 10, 1822. 
a _— Flem. Brit. An., p. 465, 1828. 
— — S. Wood, Catalogue, 1840. 
—_— — Macgill. Moll. Aberd., p. 303, 1843. 
— _ Lovén. Ind. Moll. Scand., p. 43, 1846. 
— —_— Alder. Cat. Moll. North. and Durh., p. 96, 1848. 
— — Forb. and Hani. Hist. Brit. Moll., vol. u, p. 77, pl. 18, figs. 8, 
8a, and pl. O, fig. 2, 1849. 
TELLIMYA — Brown. Mlust. Brit. Conch., pl. 16, fig. 23, 1827. 
ERYCINA — Recluz. Rev. Zool., p. 330, 1844. 
SpHHNTA costuLaTA. Macgill. Moll. Aberd., p. 301, 1843, fide Ford. and Han. 
