150 GASTEROPODA OF THE INFERIOR OOLlTtf. 



Limestone series (Pickering Cliff, &c). It is doubtfully quoted from the Lincoln- 

 shire Limestone in Judd's ' Geology of Rutland.' Specimens from the Cotteswolds 

 may be referred to G. vetustum or to G. granulato-costatum according to condition. 



66. Cerithium vetustum-majhs, Hudleston, 1882. Plate VIII, figs. 6 a, 6 b. 



1882. " Ciiemnitzia" vettjsta-major, Hudl. Geo]. Mag., dec. ii, vol. ix, p. 248, 



pi. vi, fig. 12. 



Description : 



Length (large size) . . . .43 mm. 



Width . . . . .10 mm. 



Spiral angle . . . .18°. 



Shell elongate, turrited ; whorls flat to subconvex, and only turrited 

 anteriorly ; about twelve in number ; suture distinct. Strong longitudinal ribs, 

 having a crescentic curve, characterise the spine. The precise apical conditions 

 are unknown. The anterior whorls have the longitudinal ribbing decussated by 

 about six spirals, producing nodes at the points of intersection. In the larger 

 specimens the last two whorls have the longitudinal ribbing less strongly marked, 

 whilst the spiral ribbing towards the posterior margin becomes more pronounced, 

 presenting somewhat the appearance of a nodular varix, which much increases 

 the turrited aspect of the shell. 



The base is strongly ribbed spirally. The aperture is somewhat widely ovate ; 

 and some specimens give evidence of a tolerably long anterior canal, but slightly 

 reflexed. 



Relations and Distribution. — It is by no means improbable that Cerithium 

 jiexuosum, Miinst., represents the apical conditions of this species. It is closely 

 allied to the larger varieties of Melania undulata, Deslong., whilst the typical 

 Cerithium vetustum of the Scarborough Limestone, &c, is its attenuated repre- 

 sentative on a higher horizon. 



In Yorkshire the larger shells are confined for the most part to the principal 

 shell-bed of the Dogger, but it is seldom that the ornaments are in a good state of 

 preservation. In some of the other parts of the Dogger these are better pre- 

 served, but on the whole smaller. 



