H6 MOLLUSCA FROM THE CRAG. 



Shell small, cylindrical, thick, strong, and glossy, transversely rugose ; anterior 

 extremity open, margin thickened or annulated; posterior end with an eccentric, 

 obtusely-pointed clausum. 



Length, \ of an inch. 



Locality. Cor. Crag, Sutton. Recent, Britain. 



This shell is not very abundant. The closed termination is obliquely truncate and 

 obtusely pointed, precisely resembling the recent species in that character, but my Crag 

 specimens are not so deeply or regularly ridged or annulated ; and in ten recent 

 individuals that I possess there is no thickened margin at the anterior or open termi- 

 nation, although they are quite as large, and appear to be full-grown specimens. The 

 greatly enlarged figure represents the posterior termination with its obtuse clausum. 



2. C^CUM MAMMILLATUM. 8. Wood. Tab. XX, fig. 4, a b. 

 CJECUM MAMMILLUM. S. Wood. Catalogue, 1842. 

 car. SUBULATUM, t. 20, fig. 4, b. 



C. Testa tereti, arcuatd, subcylindricd, crassd, Icevigatd, politd; antice apertd, marginatd; 

 postice clausd; clauso mammillato, excentrico. 



Shell tubular, curved, subcylindrical, strong, smooth, and glossy ; anterior extre- 

 mity open, annulated, or marginated ; posterior extremity with an elevated, mammilli- 

 form, projecting, excentric clausum. 



Length, \ of an inch. 



Locality. Cor. Crag, Sutton. 



Although this species is exceedingly abundant in the Coralline Crag, I have as yet 

 been able to obtain it only from one locality. From its perfectly smooth and glossy 

 exterior, as well as from the elevated and papilliform character of its clausum, I have 

 considered it to be distinct. The shell is thickened a little behind the margin, which 

 is somewhat thin and sharp, and one specimen has what appears to be the remains of 

 coloured bands, as if the shell, when recent, was not quite white. The mammillated 

 and projecting portion of the closed termination is near the outer or curved side of the 

 shell, and stands up prominently to a considerable height. The general form of this 

 species is nearly cylindrical, with the diameter of the closed end almost equal to that of 

 the other, but some specimens are of a subulate or tapering shape, having the diameter 

 of the open end more than twice that of the closed one, which induced me at one time 

 to consider it a distinct species (fig. 4 ), but a slightly tapering form may be also 

 observed in some of the specimens of C. trachea. The thickened margin is, I imagine, 

 the result of age, and not a specific character. 



