BIVALVIA. 239 



3. ABRA PRISMATICA, Montague. Tab. XXII, fig. 13, a, b. 



LIGULA PRISMATICA. Mont. Test. Brit. Supp., p. 23, pi. 26, fig. 3, 1808. 

 Brown. Illust. Conch., Gt. Brit., pi. 14, fig. 5, 1827. 

 Forb. Rep. ./Egean. Invert., p. 181, 1843. 



ABRA "Leach." Lamk. Hist, des An. s. Vert., torn, v, p. 492, 1818. 



MYA Turt. Conch. Diet., p. 103, 1819. 



SYNDOSMYA Recluz. Rev. Cuv. Zool., p. 367, 1843. 



Lov6n. Ind. Moll. Scand., p. 45. 



Forb. and Hani. Hist. Brit. Moll., vol. i, p. 321, pi. 17, fig. 15. 

 TELLINA STRICTA. Broc. Conch. Foss. Subap., p. 515, t. 12, fig. 3, 1817. 



DONACIFORMIS. Nyst. Rech. Coq. Foss. d'Anv., p. 5, pi. 1, fig. 17, 1836. 

 LIGULA Id. Coq. Foss. de Belg., p. 92, pi. 4, fig. 9, 1843. 



AMPHIDESMA PRISMATICUM. Turt. Brit. Biv., pi. 5, fig. 3, 1822. 

 EHYCINA ANGULOSA. "Bronn" Phil. En. Moll. Sic.,- vol. ii, p. 9, 1844. 



Spec. Char. Testa elongato-ovatd, inaquilaterali, Icevigatd, tenui ; later e postico duplo 

 breviore,- subrostrato ; dentibus lateralibus elongatis. 



Shell elongately ovate, inequilateral, smooth, and very thin ; posterior side half the 

 length of the anterior, and pointed ; lateral teeth elongated. 



Length^ \ inch. Height, |- inch. 



Locality. Cor. Crag, Sutton. 



Clyde Beds. Recent, ^Egean, British, and Norwegian Seas. 



I have met with this shell only in the Cor. Crag, and there not very abundantly. 

 If there be any difference between this and the existing form, it is that the 

 fossil appears rather the more tumid of the two. The ligamental area is small, and 

 there are two small lateral denticles or dorsal elevations in the left valve, rather 

 remote from the umbo, with one cardinal tooth ; and two lateral denticles, and 

 two cardinal teeth in the right valve ; palleal impression not visible. The siphonal 

 side is somewhat pointed and slightly compressed, forming an obscure angle or 

 ridge on that side from the umbo to the posterior extremity. This species in the 

 living state is said to have a vertical range of 100 fathoms, with a wide geographical 

 extension from Norway to the ^Egean, and there appears very little doubt that the 

 fossil called Erycina angulosa, from the Upper Tertaries of Calabria, belongs to the same 

 species. It is found also in the Belgian Crag of Anvers. Ligula fragilis, Bosquet, 

 'Bull, de 1'Acad. Roy.,' torn, xviii, pi. 11, p. 305, fig. 1, a d, a shell from Klein 

 Spauwen, strongly resembles our species, but it is, I believe with that author who has 

 pointed out the differences between the Belgian shells, quite distinct. Amphidesma 

 subreflexa, Conrad, p. 37, pi. 19, fig. 6, if one might judge from the figure alone, may 

 perhaps be united with A. prismatica. 



