GASTEROPODA. 69 



Sect. a. DEXTRAL. 



1. Cerithium TRiciNCTUM (?). Broc. Tab. VIII, fig. I a — 5, and 2. 



MuBEX TRiciNCTCs. Broc. Conch. foss. Subap. pi. 9, fig. 23, 1816. 

 Cerithium tricinctum. Nysf. Coq. foss. de Belg. p. 539, pi. 42, fig. 7, 1844. 



— Dujardin. Mem. Soc. Geol. Je France, torn, xi, p. 288, 183". 

 Cerithium punctatum. Woodward. Geol. of Norf. t. 3, fig. 29, 1833. 



— S. Wood. Catalogue 1842. 



C. Testa elongato-turritd, cequaliter gramdata ; atifractibus numerosis, planulatis, 

 triplici serie (jranulorum cinctis, columella sine plicatd. 



Shell elongato-turreted ; spire subulate and elevated ; volutions flat, ornamented 

 with three equally granulated bands ; aperture subquadrate, outer lip curved ; colu- 

 mella without a fold. 



Axis, 2 inches. 



LocalUy. Red Crag, jmssim. 



Mam. Crag. Thorpe and Bramerton. 



Although this species is common enough in the Red Crag, all the specimens I have 

 seen are in bad condition. In the Subapennine shells, and generally in those from 

 Touraine, there is a distinct fold upon the columella above, and independent of that 

 projection which forms one side of the basal canal. It is possible it may be worn 

 away in the Crag shells, as, in some specimens from the Touraine beds, which were 

 given me by Mr. Lyell, this character has quite disappeared, and it was by that alone 

 it could be distinguished. In more perfect specimens, striae or ridges on the base of 

 the volutions may be obser^-ed, which become larger toward the outer edge, like those 

 upon the Touraine shells. Specimens are sometimes found with four bands, while 

 others have only two. Some are so much eroded and altered as to have the volutions 

 distinctly convex. 



Fig. 1 {a) is from the Mam. Crag, Thorpe. 



1 (jj) from the Red Crag, Sutton. 



2 is an eroded specimen, with very convex volutions, and is probably only an 

 altered form of this species. 



2. Cerithium variculosum. Nyst. Tab. VIII, fig. 3, 3 a. 



Cerithium variculosum. Ay«<. Coq. foss. de Belg. p. 540, pi. 42, fig. 9, 1844. 

 Cerithium punciulum. S. Wood. Catalogue 1842. 



C. Testa elongatd,turritd, subulatd ; apice acuminatd ; anfractibus'd—\'>), convexius- 

 culis ; longitudinaliter plicatis ; transversim qundristriatis ; striis eleuatis, tubercidato 

 nodosis, labro acuta. 



Shell elongate, turreted, and regularly tapering, with an acuminated apex ; whorls 

 9 — 10, slightly convex, covered with four granulated bands; outer lip sharp; base 

 emarginate, without a canal. 



