CERITHIUM. 171 



though not very strongly marked. Fine spiral lines, somewhat wide apart, may 

 be traced in well-preserved specimens. 



Body- whorl scarcely one-third the entire length of the shell, almost smooth ; 

 aperture subovate ? Whorls ovate in section. Other indications wanting. 



Relations and Distribution. — This is a modified form of the " gradate " Gerithia ; 

 but how far these modifications are due to mineralization it is not easy to tell. 

 Until we can gauge the measure of this element of uncertainty close comparisons 

 are out of the question. Rare in the Clypeus-grit of Rodborough and in the 

 Parkinsoni-zone of Aston. 



The Abbas-Group. 



One other group, provisionally referred to Cerithium, yet remains, consisting of 

 elongate shells of considerable size, with closely fitting whorls spirally ornamented 

 (or smooth), and ovate in section. The aperture is ovate-elongate, with a long 

 anterior canal, more or less reflexed. The type of the group is Cerithium abbas. 

 It is possible that some shells heretofore referred to Fibula may belong here. It 

 may be regarded as a Neringeoid group. 



100. Cerithium atteitdm, sp. nov. Plate X, figs. 9 a, 9 b. 



Description : 



Length of a full-sized specimen . . 48 mm. 



Width of same . . . .12 mm. 



Length of body-whorl to entire shell 1 . . 28° : 100. 



Spiral angle . . . .16°. 



Shell elongate, scarcely turrited ; spiral angle regular. Whorls about sixteen, 

 flat in the posterior part of the spire, sub tumid in the anterior portion. The width 

 of a whorl is equal to its height plus the height of the preceding whorl. Slight 

 traces of spiral lines or belts are noticeable in the earlier whorls, but not so in the 

 later ones, which are smooth and subconvex. 



Body-whorl relatively short, smooth, and subtumid. Aperture ? ovate, with a 

 long anterior canal considerably reflexed. Whorls in section squarishly ovate. 



Relations and Distribution. — The evidently rolled condition of all available 

 specimens makes me rather cautious about instituting comparisons based on the 

 external appearance of the shell. It clearly belongs to what I have ventured to 

 call the Nerinasoid group of Cerithia. Cerithium multivolutum ) Piette (' Bull. Soc. 



1 The canal is included in this measurement. 



