BIVALVIA. 165 



America; though not numerous in species, they are widely distributed. They 

 are all marine, and probably, from the thickness of their shells, were inhabitants 

 of not very deep water. The animal is said to be occasionally fixed by a byssus, 

 though that is seldom the case, as, generally, the valves are capable of being 

 perfectly closed. 



It does not appear to be a very ancient genus, though largely developed in the 

 Tertiaries. 



1. CARDITA SENILIS, Lamarck. Tab. XV, fig. 1 a -f. 



VENERICARDIA SENILIS. Lam. Ann. du Mus., t. vii, p. 57. 



Id. Hist, des Env. de Par., p. 222. 



Desk. 2d ed. Lam., Hist, des An. a. Vert., t. vi, p. 384, 1835. 

 Parkinson. Org. Rem., vol. iii, p. 191, pi. xiii, figs. 15, 17, 1811. 

 J. Sow. Min. Conch., t. 258, figs. 13, 1820. 

 Nyst. Rech. Coq. Foss. d'Anv., p. 11, No. 43, 1835. 

 Lyell. Trans. Geol. Soc., 2d ser., vol. v, p. 245, fig. 1, 1836. 

 ANTIQUATA. Leathes' MS., fide J. Sowerby. 



INTERMEDIA? Dubois. Wolh. Podol., p. 61, pi. v. figs. 20-1, 1831. 

 CARDITA SQUAMULOSA. Nyst. Coq. Foss. de Belg., p. 207, pi. xvi, fig. 4 b, and fig. 5 a, b, 



1844. 

 Dale. Hist, and Antiq. of Harw., p. 291, t. xii, fig. 4, 1730. 



Spec. Char. Testa oblique-cordatd, incequilaterali, oblongd, sub-quadratd vel orbiculari ; 

 compressd vel turgidd, crassd, dausd ; costis 17 20 magnis, convexis, rugosis, inter dum 

 squamis, elevatis, fornicatis, asperis; lunuld parvd, impressd, dentibus crassis, perpendicu- 

 lariter striatis. 



Shell obliquely heartshaped, inequilateral, oblong, subquadrate, or orbicular, 

 tumid or compressed, thick, strong, and closed, furnished with 17 20 large, convex, 

 rugose costse, sometimes ornamented with distant, arched, and elevated squamae ; 

 lunule small, deeply impressed, teeth thick, and striated in a vertical direction. 



Largest Diameter, If inches. 



Localities. Cor. Crag, Ramsholt, Button, Sudbourne, and Gedgrave. 



Red Crag, Sutton, Newbourn, Alderton, Bawdsey, Felixstow. 



At Gedgrave it may be procured by hundreds, and occasionally with the valves 

 united, when it forms one of our handsomest shells. It appears to have flourished in 

 great profusion during the period of the Coralline Crag; and from the large number of 

 specimens met with in the Red Crag, it may probably have extended its existence into 

 the period of that deposit, although I have not yet found it at Walton-on-the-Naze.* 



This is also one of the most variable of the whole class of Bivalves. The shell 

 with this name, as given from the Environs of Paris by Lamarck, is probably an error, 

 at least I have not been able to see an Eocene species with which it could be identified ; 



* Dale gives it from Harwich, but as a shell of rare occurrence. 



