CERITHIUM. 161 



83. Cerithium lim^forme, Bomer, 1836, var. Pontonis, sp. nov. Plate IX, fig. 7. 

 1836. Cerithium LiMiEFOEME, Rom. Ool. Greb., tab. xi, fig. 19, p. 142. 



Bibliography, Sfc. — Romer's species was originally described and figured from 

 the Coral Rag of Hoheneggelsen. Morris and Ljcett referred to G. limceforme 

 and to C. quadricinctum, Miinst., a similar group of shells occurring in the Great 

 Oolite of Minchinhampton. Subsequently Lycett (' Suppl.,' p. 122) observed that 

 what the authors of the ' Great Oolite Mollusca ' had regarded as two separate 

 forms must be united into one species, and to this he assigned the name of 

 G. quadricinctum, Miinst. The figure in Goldfuss is not very like either the 

 Ponton or the Minchinhamptom fossils. On the other hand, there cannot be any 

 doubt that the Ponton shells are closely related to C. limseforme, Rom., a name 

 which in a certain sense is applicable to the entire group now under consi- 

 deration. 



Description : 



Length . . . . .10 mm. 



Width . . . . .3 mm. 



Length of body- whorl to entire shell, about . 33 : 100. 



Shell small, subelongate, scarcely turrited ; spiral angle very convex. The 

 apex is blunt; number of whorls about ten, flattish ; suture rather open. The 

 subapical whorls exhibit two to three tuberculated spirals, and the tubercles on the 

 two upper rows have a tendency to coalesce axially so as to produce costse. In the 

 anterior whorls the two upper spirals are strongly tuberculate, and have the effect 

 of producing a kind of zone. The number of spirals varies, but is three or four. 

 In some cases where there are four the third is faint, as in G. Beanii. 



The body-whorl is about one-third the length of the entire shell, and similarly 

 ornamented with spiral lines on the base. Aperture sub-oblong, with a broad, 

 short anterior canal. 



Relations and Distribution. — This particular variety of the limaforme-growp is 

 distinguished by its slender shape and somewhat more delicate ornamentation 

 both from G. Beanii on the one hand, and from 0. Wansfordias on the other. It 

 is the prevailing form at Ponton, but met with sparingly elsewhere in the 

 Lincolnshire Limestone. The Minchinhampton forms, referred by Lycett to 

 C. quadricinatum, Miinst., are on the whole more slender, less markedly pupoid, 

 and finer in their ornamentation. Although the bulk of the specimens of 

 C. Pontonis are more irregular in ornamentation, and have a slight tendency to 

 the cingulate arrangement, there are specimens from Ponton which can in no way 

 be distinguished from specimens of C. limseforme occurring in the type locality of 

 Hoheneggelsen. 



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