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 Linnzeus 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. Luctna BOREALIS, Linneus. Tab. XII, fig. 1 a, 6. 
VENUS BOREALIS. Linn. Syst. Nat., ed. 12, p. 1134, No. 143, 1767. 
_ — Don. Brit. Shells, vol. iv, t. 130, 1803. 
— EXOLETA #QUILATERA. Chem. Conch. Cab., t. vii, p. 22, t. 38, fig. 406, 1784. 
— spuRIA. Gmel. Syst. Nat., p. 3284, No. 72, 1788. 
— —_— Dillw. Dese. Cat. Rec. Shells, p. 194, 1817. 
— crrcinata? Broce. Conch. Foss. Subap., p. 552, t. 14, fig. 6, 1814. 
TELLINA RADULA. Mont. Test. Brit., p. 68, 1803. 
— —_ W. Wood. Ind. Test., p. 21, pl. 4, fig. 71, 1825. 
Lucina RapuLa. Turt. Brit. Biv., p. 116, 1822. 
= — Phil. En. Moll. Sic., p. 35, t. 3, fig. 17, 1836. 
= — Gould. Invert. Massach., p. 69, 1841. 
— _ Maegill. Moll. Aberd., p. 255, 1843. 
— _ Dekay. Nat. Hist. New York Zool., pl. 26, fig. 274, 1843. 
— apa. Turt. Brit. Biv., p. 114, t. 7, figs. 6, 7, 1822. 
— anriauaTa. J. Sow. Min. Conch., t. 557, fig. 2, 1827. 
= — Woodward. Geol. of Norf., p. 43, 1833. 
= — Nyst. Coq. Foss. de Belg., p. 128, pl. 6, fig. 7, a, 6, 1844. 
— contracta? Say. Journ. Acad. Nat. Sc., vol. iv, p. 145, pl. 10, fig. 8. 
— — ? Conrad. Am. Mioc. Foss., p. 40, pl. 20, fig. 5, 1838. 
—  ianprica. Nyst. Coq. Foss. de Belg., p. 127, pl. 6, fig. 6, a, 6, 1844. 
—  sorpatis. Lovén. Ind. Moll. Scand., p. 38, 1846. 
— Alder, Cat. Moll. North. and Durh., p. 91, 1848. 
~— — Forb. and Hanl. Hist. Brit. Moll., vol. ii, p. 46, pl. 35, fig. 5, and 
pl. M, fig. 6, 1849. 
— wmitis. Woodward (not Sow.). Geol. of Norf., p. 43, 1833. 
Spec. Char. Testa orbiculari, lenticulari, compressiusculd ; striis concentricis nume- 
rosis, erectis, approximatis vel distantibus ; anticé rotundatd, posticé subquadratd, lunuld 
lanceolata, cardine bidentato. 
Shell orbicular, lenticular, somewhat compressed, covered with numerous con- 
centric, erect strie or ridges, close or distant: anterior side rounded, posterior of a 
squarish outline, lunule small, elongate, hinge with two cardinal teeth. 
