BIVALVIA. 25 
Shell orbicular, subpellucid, inequivalved or somewhat plano-convex, equilateral, 
externally covered with fine longitudinal rays, visible only near the margin, and beau- 
tifully sculptured with diverging or divaricating strie, auricles unequal. 
Diameter, 2 inches. 
Locality. Cor. Crag, Ramsholt, Sudbourn, and Gedgrave. 
This beautiful species is exceedingly abundant at the latter locality, where, how- 
ever, the valves are always separated. At Ramsholt, they are somewhat less abun- 
dant, and the valves are there found in their natural position. 
From the figure and description given by M. Nyst, above referred to, there is little 
doubt, that the English Crag shell is the same as the one found in the Campinian 
beds of Belgium. Our shell is very thin, but strong, with irregularly-marked lines of 
increase ; the right valve always more or less flattened, while the opposite one is 
tumid or convex. Auricles very unequal and rayed, or costated, with a moderate 
sized opening beneath the anterior one of the right valve, this is almost obliterated in 
the adult shell, a rather large triangular cartilaginous area overhanging or projecting 
into the interior. The impression formed by the edge of the mantle parallel with the 
margin, and extending to about two thirds the length of the shell, that by the 
adductor, less distinctly defined. The contour of the shell is nearly circular, a little 
interrupted with a pair of rather high shoulders. A dark line diverges from the umbo, 
within which the shell is of a lighter colour, like that in P. corneus, bemg, however, 
perfectly distinct from that species. The beautifully curved or divaricating strie 
(from the absence of longitudinal or radiating ribs), are visible upon the smooth sur- 
face of the shell with the naked eye. An American fossil, Pecten Virginianus, 
Conrad. ‘Foss. of the Med. Tert. of the United States,’ p. 46, pl. 21, fig. 10, 1838, 
appears to resemble our shell in many characters, but from the representation it differs 
in being longer than high, and has the ears more equal and larger. 
3. PEcTEN simILis, Laskey. Tab. V, fig. 4, a—c. 
Prcormn siminis. Laskey. Mem. Wern. Soc., vol. 1, p. 387, pl. 8, fig. 8, 1811. 
— —_— Brown. Mlust. Conch. Gr. Brit., pl. 32, figs. 5, 6, 1827. 
— —— Flem. Brit. An., p. 384, 1828. 
— — Forb. Rep. on Egean Invert., p. 183, 1848. 
oa _ Alder. Cat. Moll. North. and Durh., p. 77, 1848. 
== _ Forb. and Hanl. Hist. Brit. Moll., vol. ii, p. 293, pl. 52, fig. 6, and 
pl. 8, fig. 1, 1849. 
OstREA TUMIDA. Turt. Conch. Dict., p. 132, 1816. 
PECTEN TUMIDUS. Turt. Brit. Biv., p. 212, pl. 17, fig. 3, 1822. 
_ — Flem. Brit. Anim., p. 384, 1828. 
— — Thorpe. Brit. Mar. Conch., p. 117, 1844. 
— _ S. Wood. Catalogue, 1840. 
— — Lovén. Ind. Moll. Scand., p. 36, 1846. 
— — G. B. Sow., Jr. Thes. Conch., vol. i, p. 57, pl. 13, figs. 27—29, 1847. 
— vyemmus? Phil. En. Molly Sic., vol. ii, p. 61, 1844, (not Goldf.) 
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