BIVALVIA. 237 
ABRA,* Leach. 1819. 
Texiina (sp.) Poli. 1791. J. Sow. Erycrya (sp.) PAil. 1836. 
Lieuta (sp.) Mont. 1803. Synposmya. Recluz, 1843. Lovén, 1846. 
AMPHIDESMA (sp.) Lamk. 1818. Forbes and Hanley, 1848. 
ABRA. Risso, 1826. Gray, 1851. Cumminela (sp.) G. B. Sow. 
Macrtra (sp.) W. Wood, 1825. 
Generic Character. Shell thin, transversely elongate, more or less inequilateral ; 
surface smooth, and in: the recent state covered by an epidermis. Hinge furnished 
with one or two small cardinal, and two distinct lateral teeth ; cartilage placed in an 
oblique, spoon-shaped process, projecting inward; ligament small, external. 
Animal of the form of the shell, with the edges of its mantle disconnected through- 
out, and finely fringed; siphons sometimes very long, slender, and separated the 
entire length, with simple orifices ; foot large, and somewhat geniculated or bent. 
This genus is closely allied to the preceding one, the ligament and cartilage being 
distinctly separated; but it differs otherwise in the arrangement of the hinge, the 
shells of this group being furnished with distinct lateral teeth. 
The shells are generally small, thin, and colourless, with an unequal degree of 
tumidity in the two valves on the posterior portion, and a difference in form, conse- 
quently, in the sinus of the mantle mark. 
In the recent state, the species live in sand and mud, have a vertical range of 
150 fathoms, and extend from the coast of Norway to the Mediterranean. 
1. ABRA ALBA, V. Wood. Tab. XXII, fig. 10, a, 6. 
Macrra atBa. W. Wood. Linn. Trans., vol. vi, pl. 16, figs. 9—12, 1802. 
— Boystt. Mont. Test. Brit., p. 98, pl. 3, fig. 7, 1803. 
TELLINA PELLUCIDA? Broc. Conch. Foss. Subap., p. 514, t. 12, fig. 8, mala. 
AmPIDESMA Boysut. Turt. Brit. Biv., p. 53, pl. 5, figs. 4, 5, 1822. 
— — Smith. Mem. Wern. Soc., yol. viii, p. 93. 
— ALBUM. Flem. Brit. An., p. 432, 1828. 
— SEMIDENTATA? Scacchi. Catalogue, p. 5. 
Erycina Rentert? Phil. En. Moll. Sic., vol. i, Pomlairia Us ties O- 
Synposmya ALBA. Receluz. Rev. Cuv. Zool., p- 362, 1843. 
— — Lovén. Ind. Moll. Scand., p. 44, 1846. 
— — Forb. and Hanl. Hist. Brit. Moll., vol. i, p. 316, pl. 17, figs. 12—14, 
1848. 
Licuta Boys? Forbes. Aigean. Invert., p- 180, 1843. 
— aLBa. WNyst. Cog. Foss. de Belg., p. 93, pl. 3, fig. 14, 1844. 
ABRA — Gray. List. Brit. Moll., p. 43, 1851. 
* Etym. a#pés, thin, delicate. 
