30 MOLLUSCA FROM THE CRAG. 
This is quite distinct from any of the varieties of P. tigrinus, the larger or more 
rounded form of the rays, as well as less inequality in the auricles, will distinguish 
it; and in all the varieties of that species, strongly marked divaricating strize, or 
curved lines radiating from the umbo, may easily be observed, but I have been unable 
to detect such markings upon my specimens of this species, although individuals of 
tigrinus, much less in size, exhibit them distinctly ; and it seems also to be specifically 
different from P. Dumasii, in which the rays are larger, fewer, and more prominent, 
and the auricles of our shell are comparatively larger than those in that species. In 
the recent state, this is, probably, a deep water species, as Payraudeau speaks of his 
specimens having been obtained by means of the dredge. 
6. PECTEN DANICUS, Chemnitz. Tab. IV, fig. 2. 
Precten Danicus. Chem. Conch. Cab., t. xi, p- 265, pl. 207, fig. 2043, 1795. 
= = G. Sow. Thesaur. Conch., vol. i, p. 61, pl. 12, figs. 16 & 187. 
—_ — Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 288, pl. 52, figs. 1, 2, 7—10. 
— GLaBRis. Brown. Ill. Brit. Conch., pl. 32, figs. 3, 4, 1827. R 
—  Dvumasir. Payr. Cat. Moll. de 'lle de Corsi., p. 75 pl. 2, figs. 6, 7, 1826. 
— Desh. Append. Lyell’s Prine., vol. iii, p. 15, 1833. 
= _ Forbes. Rept. Hgean Invert., p. 183, 1843. 
= — Jeffreys. Aun. Nat. Hist., vol. xix, p. 313. 
—  aspersus. Desh. 2d ed. Lam., t. vii, p. 136, 1836. 
== = Phil. En. Moll. Sie. vol. i, p. 82. 1836; and vol. ii, p. 57, 1844. 
— Jamusont. Smith. Mem. Wern- Soc., vol. viii, p. 58, pl. 2, fig. 1, 1838. A 
— — Brown. Ilust. Conch. Gr. Brit., 2d edit, p. 73, pl. 25, fig. 7. 
—  SEPTEMRADIATUS. - Loven. Ind. Moll. Scand., p. 31, 1846. 
—  Trirapratus. Mull. Zool. Dan., vol. ii, p. 25, pl. 60, figs. 1, 2, (fide Loven and Desh.) 
OsTREA HYBRIDA. Gmel. Syst. Nat., p. 3318, 1788 (fide Loven). 
—_— — W. Wood. Ind. Test., p. 48, pl. 10, fig. 10, 1825. 
— TRIRADIATA. Turt. ed. Linn., vol. iv, p. 268, 1806. 
— — W. Wood. Ind. Test., p. 50, pl. 10, fig. 39, 1825. 
a SEPTEMRADIATA. Id. - - p. 268, 1806. 
—  Inrurxa. Poli. Test. Sicil., vol. i, p. 160, t. 28, figs. 4, 5. 
— CLAVATA. Id. = = - p. 161, t. 28, fig. 17. 
Prcren Psrup-Amusium. Desh. Exped. Scient. de Morea, p. 231, pl. 2, figs. 9—11, 1833. 
Ency. Meth., pl. 212, fig. 6. 
Spec. Char. Testd subrotundaté, equilaterali, radiis 5—6 rotundatis inequalibus, 
striatis ; auriculis inequalibus. 
Shell subcircular, equilateral, thin, with rounded or convex rays varying in number 
from 5 to 6 striated; auricles unequal. 
Diameter, 1 inch. 
Locality. Clyde Beds. Recent, Aigean, and Scandinavia. 
Although this species, in the recent state, has been obtained in the Aigean, as 
well as in the Mediterranean Sea, and is quoted also by Philippi as an abundant fossil 
