124 MOLLUSCA FROM THE CRAG. 



is nothing within the shell that will assist in the determination, though I am 

 strongly inclined to believe it belongs to the Coralline Crag period, and that the 

 shell was found at Gedgrave. 



The lower part of the volution, near the outer angle, is furnished with a double 

 row of tubercles, above which are two spiral threads, also tuberculated ; the whole 

 is crossed with distinct, oblique, subimbricated lines of growth, and upon the base 

 are four or five circular or rather spiral ridges, also crossed by prominent lines of 

 growth. It has a prominent tooth or projection at the lower part of the columella. 

 The shell is beautifully nacreous beneath the outer coating. 



2. Tkochus ziziphinus. Linn. Tab. XIII, fig. 9, a — h. 

 Trochus ziziphinus. Linn. Syst. Nat. p. 1231. 



— — Mont. Test. Brit. p. 274, 1803. 



— — Brown. Illust. Brit. Conch, pi. 45, fig. 16-22. 



— LjEtigatfs. J. Sow. Min. Conch, t. 181, fig. 1, 1817. 



— concavus. t. 272, fig. 1, 1823. 



— Sedgwickii. J. Sow. Syst. Catalogue 1835. 



— — Nyst. Coq. foss. de Belg., p. 380, pi. 35, fig. 20, 1844. 



— L/EVIGATUS. - - - p. 379, pi. 36, fig. 11. 



— conulus, var. /3. Phil. En. Moll. Sic. vol. i, p. 175, 1836. 



— conuloides. Lam. 2d edit. torn, ix, p. 142, 1843. 



— ziziphinus. S. Wood. Catalogue 1842. 



— PSEUDO-ZIZIPHINUS. Id. 



Tr. Testa orbiculato-conicd, obliqud ; apice acuto, granulato ; anfractibus plants aut 

 concavis ; transversim et tenuiter striatis ; ad marginem subcarinatis ; infimd facie con- 

 vened; columella obliqud ; aperturd dilatatd, tetragond. 



Shell orbiculato-conical, oblique, fragile, with an acute apex and granulated 

 spire ; sides flat or slightly concave, covered with fine, or occasionally with coarse 

 striae ; base of volution submarginate, and slightly extended, somewhat convex 

 beneath, and concentrically striated ; aperture trapezoidal. 



Axis, \\ inch ; diameter, variable. 



Locality. Cor. Crag, Sutton and Ramsholt. 



Red Crag, Sutton. Recent, Britain. 



This handsome shell is not rare, but it is difficult to obtain it in perfect 

 condition, from its extreme fragility. Nearly all my specimens are from the Coral- 

 line Crag ; they are covered with fine strise, and differ from the common form of 

 the recent T. ziziphinus, which are more or less ridged. Professor E. Forbes 

 informs me he has dredged up specimens in the Scottish Seas with the same 

 kind of fine striae, and as that is the only essential difference between our 

 shell and T. ziziphinus, they are presumed to be identical. The first three 

 or four volutions are covered with about five granular ridges, but in many 

 specimens the upper ridge is the only one on which these granulations are 

 preserved. The variety with concave sides has naturally a corresponding 

 convexity of base, and the edge of the volution slightly extended, giving 



