BIVALVIA. 137 



Generic Character. — Shell orbicular, subequilateral, equivalve, lenticular; smooth 

 or striated externally. Hinge with one or two cardinal and two lateral teeth ; the 

 latter sometimes obsolete. Muscular impressions unequal, anterior one the longer, 

 mantle mark without a sinus. Ligament internal. 



Animal of the form of the shell, mantle open in front, with the margins crenulated ; 

 foot subcylindrical, crooked, club-shaped at the extremity, one siphon. 



Although the animal is closely allied to Lucina, it appears to be entitled to 

 generic distinction, on account of the difference of position in regard to the liga- 

 ment, being wholly internal, whereas in the other it is placed externally upon a ledge 

 or fulcrum ; the reported difference in the siphonal opening is also an additional 

 reason for the separation. 



This is a recent genus, and its age, as far as it is known to me, does not extend 

 beyond the Middle Tertiaries. 



1. Loripes divaricata, Linnaus. Tab. XII, fig. 4 a, b. 



Tellina divakicata. Linn. Syst. Nat., ed. 12, p. 1120, No. 70, 1767. 



— — ? W. Wood. Ind. Test., p. 23, pi. 4, fig. 87, 1825. 



— digitaria. Poll. Test. utri. Sic, vol. i, p. 47, t. 15, fig. 15, 1791. 

 Cardium arcuatum. Mont. Test. Brit., p. 85, pi. 3, fig. 2, 1803. 



— — Mat. and Rack. Linn. Trans., vol. viii, p. 67, 1807. 

 Lucina arcuata. Flem. Brit. An., p. 442, 1828. 



— — Reeve. Conch. Icon. Lucina, pi. 11, fig. 61. 



— divaricata. Woodward. Geoi. of Norf., p. 43 (not reference). 



— — Galeotti. Me'ra. de l'Acad. Roy. de Brux., t. xii, p. 157, No. 137, 



pi. 3, fig. 18, 1835. 



— — Fori, and Hani. Hist. Brit. Moll., vol. ii, p. 52, pi. 35, fig. 3, 1849. 



— trifaria. Krynecki. Bull, des Nat. de Mosc, p. 62, No. 11, 1837. Sec. Midd. 



— commutata. Phil. En. Moll. Sic, vol. i, p. 32, t. 3, fig. 15, 1836. 

 _ _ Forbes. Rep. ^Igean Invert., p. 182, 1843. 



— — Middendorff. Malacozool. Ross., p. 566, (Mem. de l'Acad. des Sci. 



de St. Petersb., 1849.) 



— N. S. allied to divakicata. G. Sow. and S. Wood. Mag. Nat. Hist., vol. iii, 



p. 325, 1839. 

 Loripes undularia. <S. Wood. Catalogue, 1840. 



Spec. Char. Testa orbiculari, subaquilaterali, convexd, bifariam oblique striata, divari- 

 cata, cardine dentibus lateralibus munito ; margine minutissme crenulatd. 



Shell orbicular, nearly equilateral, ornamented with oblique divaricating striae ; 

 hinge furnished with lateral teeth, and the margin very finely crenulated. 



Diameter, \ an inch nearly. 



Locality. Red Crag, Sutton. 



Mam. Crag, Bramerton. Recent, Mediterranean, Britain. 



This species appears first in the Red Crag, where it is very scarce, but I believe it 

 is rather more plentiful in the Mam. Crag, though not very abundant there : as a 



18 



