BIVALVIA. 53 



Mytilus flaws. PoH. Test. Sic, vol. ii, p. 207, pi. 32, fig. 4, 1/9."). 



SAGITTATUS. Id. - - - 208, - figs. 2, 3. 



UNGULATUS. Id. - - - 209, - fig. 5. 



— GALLOPROViNCiALis. DesA. 2d ed. Lam., t. vii, p. 46. 



ABBREVIATUS. Id. - - - p. 47, No. 30. 



RETUSUS. Id. - - - p. 48, - 31. 



— BOREALis. Dekmj. Nat. Hist. New York Zool., p. 182, pi. 13, fig. 222. 



— DiLATATUS. W. TVood. Ind. Test. Sup., pi. 2, Mytil., fig. 2. 



— suBSAXATiLis. Williaimon. Mag. Nat. Hist., 1834, vol. vii, p. 354, fig. 48, a — d 



— ANGULATUS. Alder. MSS., fide Williamson. 



— soLiTAEius. Rev. W. Mark. MSS. Id. 



— NOTATUs. Bekay. Nat. Hist. New York Zool., p. 182, pi. 13, fig. 223, 1843. 



— ANTiauoBUM. J. Sow. Min. Conch., t. 275, figs. 1-3, 1821. 



— — Besh. 2d ed. Lam., vii, p. 54, 1836. 



— Nyst. Rect. Coq. Foss. Prov. d'Auv., p. 17, No. 66, 1835. 



— ■ — Phil. En. Moll. Sic, vol. i, p. 73, and vol. ii, p. 53. 



— — Nyst. Coq. Foss. de Belg., p. 267, pi. 21, fig. 1, a—b. 



— — Basterot. Mem. Geol. des Env. de Bord., p. 78, 1825. 



— — Woodward. Geol. of Norf., p. 44, t. 2, fig. 20, 1833. 



— AL,«FOEMis. J. Sow. Min. Conch., t. 275, fig. 4, 1821. 

 _ _ Woodtvard. Geol. of Norf., p. 44, 1833. 



— AFFiNis. Bean. MSS. (not Sowerby). 



— PLEBEius ? Bubois de Montj). Conch. Foss. de Wolhyn. Podol., p. 69, pi. 7> 



figs. 26-28, 1831. 



— EDULis. Brocchi. Conch. Foss. sub. Apen., p. 584, 1814. 



— — Bast. Mem. Geol. des Env. de Bord., p. 79, 1825. 



Spec. Char. Testa elongato-trigonuld, lavigatd ; anterius curvcl, suhangulatd ; postarius 

 retusd ; versus basim tumidd ; dentibus tribiis vel giiaternis. 



Shell elongate, of a subtrigonal form, smooth, anterior part curved, subangulated, 

 posterior obtuse, tumid towards the base, hinge with three or four denticles. 



Greatest diameter, 4 inches. 



Locality. Red Crag, Sutton, Bawdsey, Ipswich. 

 Mam. Crag, Bramerton, Bridlington. 



Recent, Mediterranean, Britain, Scandinavia, and North America. 



The true edible species is first seen in the Red Crag Deposit, and is found in some 

 places, as might be expected, in great abundance, but the specimens have become so 

 thin and fragile, as to be with difficulty procured entire. 



What is considered as the normal form of this species, by Messrs. Forbes and 

 Hanley, is that variety which has been erected into a distinct species by Mr. 

 Williamson, under the name subsaxatilis. In this the shell is more angular, and the 

 posterior portion becomes broader, its solitary habits giving free scope to an expansion 

 at that part, and enabling it to assume what may be called its natural shape. This 

 variety has not been met with by myself in the Red Crag, but it is by no means 

 imcommon in^the deposit at Chillesford which rests upon it, and which probably 

 belongs to the mammaliferous or more recent period, and where it is the only 



