76 MOLLUSCA FROM THE CRAG. 
1. Arca TETRAGONA, Poli, Tab. X, fig. 1, a—d. 
ARCA TETRAGONA. Poli. Test. Sic., vol. ii, p. 137, pl. 25, figs. 12, 13, 1793. 
— — Turt. Brit. Biv., p. 166, pl. 13, fig. 1, 1822. 
= _— Payr. Cat. Moll. Cors., p. 61, No. 105, 1826. 
— — Desh. 2d ed. Lam., t. vi, p. 461, 1835. 
_— — Forbes. Malac. Monen., p. 41, pl. 3, 1838. 
a _ Id. Report on Agean Invert., p. 181, 1843. 
— — Phil. En. Moll. Sic., vol. i, p. 57, 1836. 
— = Reeve. Conch. Icon. Monog. Area, pl. 15, fig. 100, a—é. 
_ — 2? Menke. Moll. Nov. Holl. p. 37, No. 208, 1843. 
— Nom. Mont. Test. Brit., p. 139, pl. 4, fig. 3, 1803. 
— — Don. Brit. Shells, vol. v, pl. 158, figs. 1, 2, 1804. 
— — Brown. Brit. Conch. Mlust., pl. 25, figs. 1-3, 1825. 
— — __ S. Wood. An. and Mag. Nat. Hist., vol. iv, New Series, p. 231, pl. 13, figs. 2, 
& 2a, 1840. 
— — Morris. Cat. of Brit. Foss., p. 78, 1843. 
— rusca. Mont. Test. Brit. Sup., p. 51, 1808 (not Reeve). 
— — W. Wood. Ind, Test., p. 45, pl. 9, fig. 14, 1825. 
- — Flem. Brit. An., p. 397, 1828. 
— —_ Thorpe. Brit. Mar. Conch., p. 101, 1844. 
— carpissa. Desh. 2d ed. Lam., t. vi, p. 463, 1835. 
= — Alder. Cat. Moll. North. and Durh., p. 79, 1848. 
— wNavicutaRis. Desh. 2d ed. Lam., t. vi, p. 462, 1835. 
—_ — Phil. En. Moll. Sic., vol. ii, p. 42, 1844. 
— = Lovén. Ind. Moll. Scand., p. 33, 1846. 
— Brrrannica. Reeve. Conch. Icon. Monog. Arca, pl. 15, fig. 98. 
—- — Nyst. Tab. Syn. des Arches. Viv. et Foss., p. 14, No. 47, 1847. 
— papiLLosa. Smith. Mem. Wern. Soc., vol. vii, pl. 1, fig. 19, 1838. 
Batanus Benton. List. Hist. Conch., lib. iii, fig. 207, 1687. 
Ency. Meth., pl. 308, fig. 3, a—d. 
Spec. Char. Testdé oblongd, valde inequilaterd, costato-striatd, et transversim 
decussatd, antice rotundatd, postice angulatd ; carind posticd eminente, acuta ; apicibus 
remotis incurvis ; margine ventral: hiante. 
Shell oblong, very inequilateral, with costated striz, decussated by distinct lines 
of growth; anterior side rounded, posterior angulated, with a prominent keel or 
ridge from the umbo to the posterior ventral margin ; umbones distant, incurved ; 
ventral margin gaping. 
Largest diameter, \ inch. 
Locality. Cor. Crag, Sutton, Ramsholt, and Sudbourn. 
Red Crag, Sutton. Recent, Scandinavia, Britain, and Mediterranean. 
Very small specimens are by no means rare in the Coralline Crag; but I have met 
with very few examples of the adult shell. These small or young specimens are very 
regular in form, being much elongated transversely, of a somewhat rhomboidal shape, 
the anterior side slopes a little from the extremity of the hinge line, rounding at the 
ventral margin, while the posterior side is angular, pointed and projecting ; the ventral 
