CERITHINELLA. GO 



Cryptaulax tortilis (Heb. and Desl.). Plate VII, figs. 12, 13. 



1860. Cerithium tortile, Hebert and Deslongchamps, Ball. Soc. Linn. Normand., vol. v, p. 191, 

 pi. vi, fig. 6. 



Type. — Length to breadth, 3^. Shell twisted, pointed, with a polygonal twisted 

 spire ; whorls slightly rounded, showing a variable number of angles, generally six 

 or seven. Sutural furrow broad and rather deep. Each whorl is marked with two 

 transverse (spiral) ridges placed before and behind. The interval is marked with 

 much smaller parallel ridges, variable in number. Angles of the whorls arranged 

 in a more or less pronounced spiral series. In the Oxfordian of Montreuil-Bellay. 



Description. — The length of the figured specimen (PL VII, fig. 12) is 15 mm., 

 and its maximum breadth is about 4 mm. The spiral angle, 15°. Thirteen whorls 

 preserved, of which the first two only are smooth. The two bounding ribs and 

 one intermediate rib commence together. The second intermediate rib commences 

 in the seventh whorl anteriorly to the first, but no more appear. The base has 

 five spirals more, and then they are less influenced by the longitudinals posteriorly. 

 There are thirteen longitudinal rows in the last whorl. The suture line is undu- 

 lating. The aperture is somewhat imperfect in the specimen, but is well shown in 

 another. Fig. 13 exhibits the generic characters of the "peristome broadly reflexed 

 upon the left lip " and the " posterior canal in the angle," etc. 



Relations. — Roughly speaking, the shells from the Inferior Oolite, referred by 

 Hudleston to this species, may belong to it ; but as they differ in some respects of 

 an importance equal to that which is often made to separate forms in this class of 

 shell, they can be considered perhaps as the ancestors only of shells from which 

 the latter are mutations. These differences are a wider spiral angle, less deep 

 suture which is not thrown into curves by the overlapping of the marginal knobs, 

 and the greater equality of the knobs in each longitudinal group. 



Distribution. — Nearly forty specimens of this have been seen associated at 

 Shipton-on-Cherwell. In the collection of Mr. W. H. Hudleston. 



Genus CERITHINELLA, Gemmellaro. 



The genus is defined by the author as follows : Shell turreted, slender, whorls 

 numerous, flat, ornamented Avith spiral ribs or rows of small nodes ; aperture quad- 

 rilateral, with a very faint canal. 



