282 MOLLUSCA FROM THE CRAG. 
Panopea ArcTICA. Gould. Inv. Massach., p. 37, fig. 27, 1840. 
—- — Dekay. Nat. Hist. New York Zool., p. 246, 1843. 
— — King. Ann. and Mag. Nat. Hist., vol. xviii, p. 243, 1846. 
Panopma Bivona. J. Smith. Wern. Mem. vol. viii, p. 107, pl. 2, fig. 4, 1839. 
_— — Phil. En. Moll. Sic., vol. i, p. 8, t. 2, fig. 1, a—e, 1836. 
_ SpenGueRt. Valen. Arch. du Mus., tom. i, p. 15, pl. 5, fig. 3, 1839. 
— — Chenu, Illust. Conch. Panopeea, pl. 4, fig. 2, 4,4 a, 46; pl. 6, 
fig. 3, a, 6; and pl. 10, fig. 2, a, 6. 
— Norvecica. J. Sow. Min. Conch., t. 610, fig. 2, and 611, figs. 1, 2. 
_— Lovén. Ind. Moll. Seand., p. 49, 1846. 
— — Forb. and Hani. Hist. Brit. Moll., vol. i, p. 175, pl. 11, 1848. 
— — Middend. Malacozool. Rossica (Mem. loc. cit.), p. 593, t. 20, 
fig. 11, 1849. 
Spec. Char. Testa crassa, oblonga vel subrhomboidali, plus minusve inequilateral ; 
antice plerumque breviore, portice truncatd et latiore ; cardine edentulo ? impressione pallit, 
iaterrupta, maculosa. 
Shell thick, oblong or somewhat rhomboidal, more or less inequilateral ; anterior 
side generally the shorter, posterior truncated and broader; hinge without teeth ; im- 
pression by the mantle interrupted, spotted and irregular. 
Length, 3 inches. Height, 2 inches. 
Locality. Red Crag, Sutton, Butley. 
Mam. Crag, Chillesford, Bridlington. 
Clyde Beds, and Sicily. 
Recent, North America, Britain, Scandinavia, Russian Lapland, and Sea of Ochotsk. 
As yet this shell has been but sparingly obtained from the Red Crag, but it does 
not appear to be very scarce in the native bed at Chillesford, where the valves are met 
with in their natural position. Although my specimens from the Red Crag do not 
amount in number to more than half a dozen, there is a considerable variation among 
them. 
Our fossils are in general more equilateral, that is to say, the siphonal side of the 
shell is less in size, particularly those from Chillesford, than the living specimens, or 
those from the newer Tertiaries of Sicily, where the anterior side does not constitute 
more than a third of the entire shell; there is, however, no doubt as to the identity of 
the British fossil with the recent species. Among other minor differences may be 
mentioned the ligamental fulcra, which in Crag specimens extend half way across the 
dorsal margin, giving support to large and powerful ligaments, while in the 
living shell this fulcrum is much smaller. The adductor muscle-marks are deeply 
impressed, the shell gapes widely on the posterior side, and there is a considerable 
opening in the fore part of the ventral margin for the extrusion of the foot: the 
surface is much roughened by somewhat irregular lines of growth ; and the centre of 
the shell is contracted or depressed, giving it a couple of obtuse ridges which diverge 
from the umbo. 
