BIVALVIA. 85 



giving a more ovate form to the outline. It has a rather narrow row of denticles on 

 both sides, those upon the anterior are from ten to twelve in number, with about six 

 or eight upon the shorter or posterior side. A shell somewhat resembling this is 

 found in the Upper Marine, in Headon Hill, being free from crenulations at the 

 margin, and is also a thin shell, with a similar ovate contour, though seemingly 

 rather more pointed at the posterior extremity, but my specimens of the Eocene 

 fossil are scarcely in a sufficiently good state of preservation for a fair comparison. 



A specimen of this species, found at Bridlington, was obligingly forwarded to me 

 for examination by Mr. Leckenby. 



4. NUCULA NUCLEUS, Linnaeus. Tab. X, fig. 6, a b. 



ARCA NUCLEUS. Linn. Syst. Nat., ed. 12, No. 184, p. 1143, 1767, not Brander. 

 Chem. Conch. Cab., t. vii, p. 241, t. 58, fig. 574, 1784. 

 Don. Brit. Shells, vol. ii, pi. 63, 1801. 

 Broc. Conch. Foss. Subap., vol. ii, p. 480, 1814. 

 W. Wood. Ind. Test., p. 47, pi. 10, fig. 42, 1825. 

 NUCULA NUCLEUS. Turt. Brit. Biv., p. 176, t. 13, fig. 4, 1822. 



S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 294, pi. 14, fig. 1, 



1840. 



Thorpe. Brit. Mar. Conch., p. 105, p. 74, 1844. 

 Loven. Ind. Moll. Scand., p. 34, 1846. 

 Forb. and Hani. Hist, of Brit. Moll., vol. ii, p. 215, pi. 47, figs. 7, 8, 



1849. 



MARGARITACEA. Lam. Syst. des An. s. Vert., p. 115, 1801 (mostly). 

 G. B. Sowerby. Genera, No. 17, fig. 7. 

 De Blainv. Malac., pi. 7-5, fig. 5, 1825. 



? Bast. Mem. de la Soc. d'Hist. Nat., t. 2, p. 78, No. 2, 1825. 

 Payr. Cat. Moll. Cors. p. 64, 1826. 

 Brown. Illust. Conch. Gr. Brit., pi. 25, fig. 12, 1827. 

 Dubois. Conch. Foss. Wolhyn. Podol., p. 66, t. 7, figs. 35, 36, 



1831. 



Goldf. Pet. Germ., vol. ii, p. 158, t. 125, fig; 21, a d. 

 Phil. En. Moll. Sic., vol. i, p. 64, t. v, fig. 8, 1836. 

 Bronn. Leth. Geol., vol. ii, p. 929, t. 39, fig. 5, a c, 1838. 

 Swains. Malac., p. 382, fig. 125,/ a, 1840. 

 G. B. Sow., Jr. Conch. Man., fig. 137, 1842. 

 Forbes. Report on JSgean Invert., p. 180, 1843. 

 Sism. Syn. Meth. An. Inv. Piedm. Foss., p. 15, 1847. 

 ARGENTEA? Brown. Illust. Conch. Gr. Brit., pi. 25, figs. 14, 15, 1827. 

 GLYCIMERIS ARGENTEA. Da Costa. Brit. Conch., p. 170, pi. 15, fig. 6, 1778. 

 DONAX ARGENTEA. Gmel. Syst. Nat., p. 3265, 1/88. 

 Ency. Meth., pi. 311, fig. 3, a~ b. 



Spec. Char. Testa obliqud, ovatd, transversd, subtriangulari, Icevi, aut obsolete striatd ; 

 dentibus cardinalibus acutis ; margine crenulato. 



Shell obliquely ovate, transverse, slightly triangular, smooth or obsoletely striated ; 

 hinge with numerous, sharp, and erect teeth ; margin crenulated. 



