BIVALVIA. 245 
Shell large, thick and strong; irregularly striated externally, ovately triangular ; 
inequilateral; anterior side obtusely angulated, posterior rounded; ligamental area 
large ; lateral teeth perpendicularly striated. 
Length, 25 inches. Height, 2 inches. 
Locality. Red Crag, Felixstow. 
One specimen only of this species is all that I have seen. It is from the cabinet of 
Mr. Perry, and was obligingly forwarded to me for publication by Mrs. Corder. 
It somewhat resembles JV. solidissima, Chemn. (JZ. gigantea, Lamk.), but differs from 
that shell in being much more rounded on the posterior side. The lateral teeth in our 
shell are also considerably larger, and the sinus in the mantle-mark is also different ; 
but that perhaps may depend upon, or would be modified by, the length and form of 
the posterior side. A shell in the British Museum, from South America, 47. exalbida, 
much resembles it in form, but in this latter species the lateral teeth are smooth. 
6. Mactra truncata, Montague. Tab. XXIV, fig. 2, a, 6. 
PEcTUNCULUS cRassIuscuLUS. Jist. Hist. Conch., lib. 11, fig. 87. 
Macrra truncata. Mont. Test. Brit. Supp., p. 34, 1808. 
— — Forb. and Hanl. Hist. Brit. Moll., vol. i, p. 354, pl. 23, fig. 1. 
— SUBTRUNCATA. Donov. Brit. Shells, vol. iv, pl. 126, 1803. 
— CRASSATELLA. Desh. 2d ed. Lamk. tom. vi, p. 107, No. 33, 1835. 
— crassa. Turt. Brit. Biv., pp. 69, 258, t. 5, fig. 7, 1822. 
SPIsuLA — Gray. Mag. Nat. Hist., new series, vol. i, p. 373, 1837. 
Spec. Char. Testd rotundato-triangulatd, subequilaterali crassd ; sinu palliari brevi, 
linguiformi ; umbonibus prominentibus, dentibus lateralibus perpendiculariter striatts. 
Shell roundedly triangular, subequilateral, thick; palleal sinus short, tongue- 
shaped; umbones prominent, lateral teeth with perpendicular striz or ridges. 
Diameter, 1+ inch. 
Locality, Red Crag, Sutton, Walton Naze. 
Clyde Beds. Recent, Britain, and Scottish Seas. 
This is at present a rare Crag species. A worn and somewhat injured specimen 
has long been in my possession; two others, in better condition, have since been 
obtained by Mrs. Corder, and these are all that I have seen. 
7. Mactra souipa, Linneus. Tab. XXIV, fig. 4, a—e. 
Macrra sotipa. Linn. Syst. Nat., ed. 12, p. 1126, 1766. 
—_ — Goldf. Petr. Germ., vol. ii, p. 253, No. 1, t. 152, fig. 5. 
— — Phil. En. Moll. Sic., vol. i, p. 11; vol. ii, p. 10. 
_— — Jyst. Conch. Foss. de Belge., p. 77, pl. 3, fig. 10, 1844. 
_ — Forb. and Hanl. Hist. Brit. Moll., vol. i, p. 315, pl. 22, figs. 1—5, 1848. 
