2S2 MOLLUSCA FROM THE CRAG. 



Panopea arctica. Gould. Inv. Massach., p. 37, fig. 27, 1840. 



— — DeJcay. Nat. Hist. New York Zool., p. 246, 1843. 



— King. Ann. and Mag. Nat. Hist., vol. xviii, p. 243, 1846. 

 Panopea Bivonje. J. Smith. Wern. Mem. vol. viii, p. 107, pi. 2, fig. 4, 1839. 



— — Phil. En. Moll. Sic, vol. i, p. 8, t. 2, fig. 1, a—c, 1836. 



— Spengleri. Valen. Arch, du Mus., torn, i, p. 15, pi. 5, fig. 3, 1839. 



— — Chenu. Illust. Conch. Panopeea, pi. 4, fig. 2, 4, 4 a, 4 b ; pi. 6, 



fig. 3, a, b ; and pi. 10, fig. 2, a, b. 

 Norvegica. J. Sow. Min. Conch., t. 610, fig. 2, and 611, figs. 1, 2. 



— — Lovcn. Ind. Moll. Scand., p. 49, 1846. 



— Forb. and Hani. Hist. Brit. Moll., vol. i, p. 175, pi. 1 1, 1848. 



— — Middend. Malacozool. Rossica (Mem. loc. cit.), p. 593, t. 20, 



fig. 11, 1849. 



Spec. Char. Testa crassd, oblongd vel subrhomboidali, plus minusve inaquilaterali ; 

 antice plerumque breviore, portice truncatd et latiore ; cardine edentulo ? impressione pallii, 

 interrupta, 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. 



