LACUNA SUBOPERTA. 669 



Remarks. — This shell may be distinguished from L. crassior, with which it is 

 often found, by its thinner texture, its rather longer spire with an oblique suture, 

 and its compressed and less convex whorls. Jeffreys reports it from Bridlington, 

 Kelsey Hill and Uddevalla, while A. Bell has found it in many British Pleistocene 

 deposits. As I cannot now lay my hands on any of these I have figured a recent 

 one from the Norwich Museum to enable students to recognise any specimens 

 which may turn up hereafter. 



Lacuna suboperta (J. Sowerby). Plate LIII, figs. 31, 32. 



1813. Vivipara suboperta, J. Sowerby, Miu. Couch., vol. i, p. 80, pi. xxxi, fig. 6. 



1844—81. Littonna suboperta, Nyst, Coq. foss. Belg., p. 388, pi. xxxvii, fig. 1, 1844; Conch. Terr. 



tert, Belg., p. 93, pi. vi, fig. 21, 1881. 

 1842—72. Littorina suboperta, S. V. Wood, Ann. Mag. Nat. Hist. [1], vol. ix, p. 532, 1842; Mon. 



Crag Moll., pt. i, p. 120, pi. x, fig. 13, 1848; Lacuna suboperta, 1st Suppl., pt. i, p. 80, 1872. 



1871. Littorina littorea var., Jeffreys in Prestwich, Quart. Journ. Geol. Soc, vol. xxvii, p. 489. 



1872. Littorina suboperta, A. and E. Bell, Proc. Geol. Assoc, vol. ii, p. 209. 



1874 — 92. Littorina suboperta, Van den Broeck, Ann. Soc. inalac, Belg., vol. ix, p. 273, 1874 ; Bull. 



Soc. Beige Geol., vol. vi (Mcmoires), p. 133, 1892. 

 1912. Littorina suboperta, Tesch, Med. v. d. Rijks. v. Delfstoffen, No. 4, p. 62, no. 136. 

 1892—98. Lacuna suboperta, A. Bell, Proc. Roy. Irish Acad. [3], vol. ii, p. 630, 1892 ; L. (/ Littorina) 



suboperta, Trans. Roy. Geol. Soc. Cornwall, vol. xii, p. 154. 



Specific Characters. — Shell thick and solid, ovato-conical ; whorls 5, depressed, 

 rounded and obtusely angulate at the base ; spire short, elongate ; apex acute ; 

 mouth ovate, contracted above ; inner lip forming a strong and rather wide callus 

 on the columella, covering the umbilicus, either wholly or in part. 



Dimensions. — L. 12 — 15 mm. B. 8 — 10 mm. 



Distribution. — Not known living. 



Fossil: St. Erth. : Waltonian, Newbournian, Butleyan, at most 

 localities of the Red Crag, sometimes in fair abundance. 



Scaldisien : Belgium. Poederlien : Belgium, Holland. 



Remarks. — Except that it has been found at St. Erth, this species seems to be 

 confined to the Red Crag of East Anglia and to deposits of similar age in Belgium 

 and Holland. In the Crag it makes its first appearance at Walton-on-Naze and 

 Oakley where it is fairly common, and it may be found almost everywhere at other 

 Crag horizons although more rarely. Wood pointed out that while this form is 

 thick and strong our specimens from the Crag are generally more or less mutilated, 

 but they are too numerous to lend any support to the view that they are 

 derivative from some earlier deposit. L. suboperta has not been found in 

 the Coralline Crag, though a smaller and less solid variety (which is also given 

 here, fig. 31) occurs at St. Erth. 



