BIVALVIA. 177 



smooth. In the recent state it is covered with a thick, ohvaceous, or dark coloured 

 epidermis, and at the urabones the shell is often eroded ; marks of erosion are visible 

 also, more or less, in most of the fossils.* Old specimens are generally thickened 

 within, showing deeply-indented muscle marks. There is a deeply-excavated lunule 

 on the anterior side, and a corresponding slope on the posterior dorsal margin, with a 

 prominent fulcrum for the ligament. 



It is said to be obtained in deep water in the British seas, though probably it had 

 an extensive vertical range, being found as a fossil at Bramerton, in association with 

 Littoriiia llttorea, Mytilus edulis, and others that now inhabit very shallow water ; and 

 the fossil specimens are in that good state of preservation to justify the supposition 

 that they had not been transported from any great distance. 



4. AsTARTE Basterotii, Lujonliaire. Tab. XVII, fig. 2 a — d. 



AsTARTE Basterotii. Lajonk. Not. Geol. euv. d'Auv. (Mem. delaSoc. d'Hist. Nat. dePar.), 

 t. i, p. 129, pi. vi, fig. 3«— e, 1823. 



— — Nyst. Rech. Coq. Foss. d'Anv., p. ■/, No. 2C, 1835. 



— — Id. Coq. Foss. de Belg., p. 151, pi. viii, fig. 4 a — c, 1844. 



— NiTiDA. J. Sow. Min. Conch., t. 521, fig. 2, 1826. 



— — S. Wood. Catalogue, 1840. 



Crassina NITIDA. Besh. 2d edit. Lam., t. yi, p. 258, 1835. 



Dale, Hist, and Antiq. of Harwich, t. xi, figs. 12 and 14, 1/30. 



Spec. Char. Testa transversa, ovato-trigonula, suhlavigatd, antice rotundatd, postice, 

 subangidatd natibus tenui-siilcatis ; lunuld ehngato-ovutd. ; margine crenulato. 



Shell transverse, ovately triangular, nearly smooth, anterior side rounded, posterior 

 subangulated ; umbones finely sulcated ; lunule elongate and smooth ; margin cre- 

 nulated. 



Length, Ifths of an inch; height, l|-th ditto. 



Localities. Cor. Crag, Sutton, Ramsholt, Sudbourn, Gedgrave. 



Red Crag, Sutton, Bawdsey, Felixstow, Walton-on-the-Naze ? 



The most distinguishing character of this species is a set of fine concentric ridges 

 covering the young shell, and occupying generally less than the fourth part of the 

 diameter of the surface, or a little beyond the umbones of the adult, while all the other 

 part is smooth, or at least with only visible lines of growth. f 



The general size of the most common form of the Suffolk shell is an inch in length 

 and iths of an inch in height, and it has generally then a crenulated margin, but the 

 other specimen figured (fig. 2 c, d) measures as much as an inch and |ths in length, with 

 an edge perfectly smooth ; they are all rather compressed, and have a deep, elongated 



* A recant specimen in the possession of Mr. Lowry, with the specific name of lactea attached, but 

 which I believe to be only a var. of this species, is quite free from ridges about the umbo. 



f The ridges upon the umbo of the Belgian shell are somewhat larger than those upon the British 

 specimens, and may be considered a distinct variety. 



