BIVALVIA. 139 



become obsolete : anterior muscular impression of a ligulate or elongated form. 

 Palleal impression without a sinus. Ligament external. 



The animal of this genus is described as having its mantle open in front, and 

 fimbriated edges ; very short siphonal tubes, with a long cylindrically-formed foot. 



The genus as here restricted is intended to include all those species which have 

 an external ligament, of which the Venus borealis of Linnaeus may be considered the 

 type. This appears to form a distinct group, characterised by a differently formed 

 anterior muscle, which the mantle seems to envelope, and the impression is isolated 

 within : the edge of the mantle extending up to the anterior part of the adductor, 

 and not on the posterior edge where the line of the mantle mark, in most of the 

 Dimyaria, connects the two muscles. 



1 . LUCINA BOREALIS, LinncBus. Tab. XII, fig. 1 a, b. 



VENUS BOREALIS. Linn. Syst. Nat., ed. 12, p. 1134, No. 143, 1767. 



Don. Brit. Shells, vol. iv, t. 130, 1803. 



EXOLETA .EQUILATERA. Chem. Conch. Cab., t. vii, p. 22, t. 38, fig. 406, 1784. 

 SPURIA. Gmel. Syst. Nat., p. 3284, No. 72, 1788. 



Dillw. Desc. Cat. Rec. Shells, p. 194, 1817. 



CIRCINATA? Broc. Conch. Foss. Subap., p. 552, t. 14, fig. 6, 1814. 

 TELLINA RADTJLA. Mont. Test. Brit., p. 68, 1803. 



W. Wood. Ind. Test., p. 21, pi. 4, fig. 71, 1825. 

 LUCINA RADULA. Turt. Brit. Biv., p. 116, 1822. 



Phil. En. Moll. Sic., p. 35, t. 3, fig. 17, 1836. 

 Gould. Invert. Massach., p. 69, 1841. 

 Mafffill. Moll. Aberd., p. 255, 1843. 

 Dekay. Nat. Hist. New York Zool., pi. 26, fig. 274, 1843. 

 ALBA. Turt. Brit. Biv., p. 114, t. 7, figs. 6, 7, 1822. 

 ANTIO.UATA. J. Sow. Min. Conch., t. 557, fig. 2, 1827. 

 Woodward. Geol. of Norf., p. 43, 1833. 

 Nyst. Coq. Foss. de Belg., p. 128, pi. 6, fig. 7, a, b, 1844. 

 CONTRACTA ? Say. Journ. Acad. Nat. Sc., vol. iv, p. 145, pi. 10, fig. 8. 

 ? Conrad. Am. Mioc. Foss., p. 40, pi. 20, fig. 5, 1838. 



FLANDRICA. Nyst. Coq. Foss. de Belg., p. 127, pi. 6, fig. 6, a, b, 1844. 



BOREALIS. Lovtn. Ind. Moll. Scand., p. 38, 1846. 



Alder. Cat. Moll. North, and Durh., p. 91, 1848. 

 Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 46, pi. 35, fig. 5, and 

 pi. M, fig. 6, 1849. 



MITIS. Woodward (not Sow.). Geol. of Norf., p. 43, 1833. 



Spec. Char. Testa orbiculari, lenticulari, compressiusculd ; striis concentricis nume- 

 rosis, erectis, approasimatis vel distantibus ; antice rotundatd, postice subquadratd, lunuld 

 lanceolatd, cardine bidentato. 



Shell orbicular, lenticular, somewhat compressed, covered with numerous con- 

 centric, erect striae or ridges, close or distant ; anterior side rounded, posterior of a 

 squarish outline, lunule small, elongate, hinge with two cardinal teeth. 



