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, 2| 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 M. solidissima, Chemn. (M. 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, M. 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, b. 



PECTUNCULUS CRASSITJSCULUS. List. Hist. Conch., lib. 11, fig. 87. 

 MACTRA TRUNCATA. Mont. Test. Brit. Supp., p. 34, 1808, 



Forb. and Hani. Hist. Brit. Moll., vol. i, p. 354, pi. 23, fig. 1. 



SUBTRUNCATA. Donov. Brit. Sheila, vol. iv, pi. 126, 1803. 



CRASSATELLA. Desk. 2d ed. Lamk. torn, 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. Testa rotundato-triangulatd, subcequilaterali crassd ; sinu palliari brevi, 

 lingmformi ; umbonibus prominentibus, dentibus lateralibus perpendiculariter striatis. 



Shell roundedly triangular, subequilateral, thick; palleal sinus short, tongue" 

 shaped ; umbones prominent, lateral teeth with perpendicular striae or ridges. 



Diameter, \\ inch. 



Locality. Red Crag, Button, 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 SOLIDA, Linnaeus. Tab. XXIV, fig. 4, a c. 



MACTRA SOLIDA. 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. 



Nyst. Conch. Foss. de Beige., p. 77, pi. 3, fig. 10, 1844. 

 _ _ Forb. and Hani. Hist. Brit. Moll., vol. i, p. 315, pi. 22, figs. 15, 1848. 



