CERITHIUM. 169 



Body-whorl small relatively to the spire ; aperture ? subovate, with a good-sized 

 anterior canal. 



Belations and Distribution. — The more slender spire, its less strongly tabulate 

 character, and the continuity of the costse without bifurcation, separate this 

 species from other members of the comma-group. French specimens of G. circe 

 are certainly more tabulate than the one figured, which is from the Inferior Oolite 

 of Dorsetshire, and is the only one of the kind known to me as British. 



The above constitute the comma-group as far as it is known to occur for 

 certain in our Inferior Oolite. Thus restricted, it would be seen to be confined to 

 the Upper Division. 



96. Cerithium (species or variety). Plate X, fig. 5. 



A Cerithium, apparently belonging to the comma-group, occurs very rarely in 

 the Lincolnshire Limestone at Weldon. It is about 15 mm. long, extremely 

 tabulate, and with concave whorls. The costas are numerous, short, and confined 

 to the posterior margin. But these conditions are not altogether reliable, owing 

 to peculiarities of mineralization. 



The body-whorl is angular, concave, and bicarinate ; base rather depressed ; 

 aperture subquadrate, with a well-developed anterior canal. 



The whorls are more concave than in G. comma, and the bicarination of the 

 body-whorl is another marked feature of difference. As a temporary name we 

 may distinguish this as Cerithium commaoides. 



In some respects also this form leads up to a group of Cerithia with tabulate 

 whorls and no axial ornamentation. 



97. Cerithium pergradatum, sp. nov. Plate X, fig. 6. 



Description : 



Length . . . . .20 mm. 



Width ..... 6*25 mm. 

 Spiral angle . . . .18°. 



Shell subelongate, conical, strongly turrited ; apical conditions unknown. 

 Whorls about twelve in number, flat or slightly excavated anteriorly, and increasing 

 by steps so as to overlap the suture, which is channeled. A raised rim marks the 

 posterior margin, which is spirally striated ; plain spiral lines succeed, which are 

 about six in number in the anterior whorls. 



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