76 MOLLUSCA FROM THE CRAG. 



1. Arca tetragona, Poll. Tab. X, fig. 1, a — d. 



Arca tetragona. Poli. Test. Sic, vol. ii, p. 137, pi. 25, figs. 12, 13, 1793. 



_ _ Turt. Brit. Biv., p. 166, pi. 13, fig. 1, 1822. 



_ _ Payr. Cat. Moll. Cors., p. 61, No. 105, 1826. 



— — Desk. 2d ed. Lam., t. vi, p. 461, 1835. 

 _ — Forbes. Malac. Monen., p. 41, pi. 3, 1838. 



— — Id. Report on iEgean Invert., p. 181, 1843. 

 _ _ Phil. En. Moll. Sic., vol. i, p. 57, 1836. 



— — Reeve. Conch. Icon. Monog. Arca, pi. 15, fig. 100, a — b. 



— — 1 Menke. Moll. Nov. Holl. p. 37, No. 208, 1843. 



— No;e. Mont. Test. Brit., p. 139, pi. 4, fig. 3, 1803. 



— — Don. Brit. Shells, vol. v, pi. 158, figs. 1, 2, 1804. 



— — Brown. Brit. Conch. Illust., pi. 25, figs. 1-3, 1825. 



— — S. Wood. An. and Mag. Nat. Hist., vol. iv, New Series, p. 231, pi. 13, figs. 2, 



& 2a, 1840. 



— — Morris. Cat. of Brit. Foss., p. 78, 1843. 



— fusca. Mont. Test. Brit. Sup., p. 51, 1808 (not Reeve). 



— _ W. Wood. Ind. Test., p. 45, pi. 9, fig. 14, 1825. 



— — Flem. Brit. An., p.. 397, 1828. 



— — Thorpe. Brit. Mar. Conch., p. 101, 1844. 



— cardissa. Desk. 2d ed. Lam., t. vi, p. 463, 1835. 



— — Alder. Cat. Moll. North, and Durh., p. 79, 1848. 



— navicularis. Desk. 2d ed. Lam., t. vi, p. 462, 1835. 



— — Phil. En. Moll. Sic, vol. ii, p. 42, 1844. 



— — LovSn. Ind. Moll. Scand., p. 33, 1846. 



— Britannica. Reeve. Conch. Icon. Monog. Arca, pi. 15, fig. 98. 



— — Nyst. Tab. Syn. des Arches. Viv. et Foss., p. 14, No. 47, 1847. 



— papillosa. Smith. Mem. Wern. Soc, vol. viii, pi. 1, fig. 19, 1838. 

 Balanus Bellonii. List. Hist. Conch., lib. hi, fig. 207, 1687. 



Ency. Meth., pi. 308, fig. 3, a— b. 



Spec. Char. Testa oblongd, valde incequilaterd, costato-striatd, et transversim 

 decussatd, antice rotundatd, postice angulatd ; carina posticd eminente, acuta ; apicibus 

 remotis incurvis ; margine ventrali hiante. 



Shell oblong, very inequilateral, with costated striae, 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, 1 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 



