CERITHIUM. 147 



lines in the base, though very strong, are not granulated. Specimens showing 

 the full character of the aperture are not available. 



Relations and Distribution. — Differs from G. vetustum and its varieties in a less 

 marked tendency to longitudinal ornament, *. e. that costae, as a rule, do not 

 predominate over the spiral ornamentation. Nevertheless I am scarcely prepared 

 to say that these forms do not inosculate. The Yorkshire beds contain G. muricatum, 

 more especially the lower portions of the Dogger proper. The variety named 

 trilineatum is almost worthy of being regarded as a distinct species (fig. 3). This 

 is a unique specimen from the Scarborough Limestone. 



64. Crkitiiium grmmatum, Morris and Lycett, 1853. Plate VIII, fig. 4. 



1853. Cektthitjm gemmatum, Morris and Lycett. Great Ool. Moll., p. 11 



pi. xv, fig. 6. 

 1884. — Hudleston, Geol. Mag.,dec. 



iii, vol. i, p. 58,pl. iii,fig. 9. 



Bibliography, Sfc. — The type was from the Scarborough Limestone. The 

 specimen now figured is from the Bean collection. 



Description. — Length 15 mm., width 4*5 mm., spiral angle 20°. Shell turrited ; 

 whorls about ten, rather convex, encircled with five rows of nodules ; nodules 

 ovate, twenty-four in a whorl ; the rows of nodules are slightly curved ; they are 

 oval, their longer diameter being in the axis of the shell, and they are distant from 

 each other about their own diameter. The body- whorl shows five rows of nodules 

 on the side ; the base is ornamented with spiral bands, the granules of which are 

 drawn out spirally, and less deeply cut. Other indications wanting. 



Relations and Distribution. — Differs from G. muricatum in the fact that the 

 granules are drawn out axially rather than spirally. The beaded character of the 

 granulations may be partly the result of mineralization. It occurs in the grey 

 marly Oolite of White Nab (Scarborough Limestone Series), and appears to be a 

 local form. It may have some relationship to Cerithium vetustum, inasmuch as 

 there is a tendency to axial rather than to spiral ornamentation. 



The Vetustum- Subgroup, partly included under Chemnitzia by some authors. 



This group may to a certain extent be said to inosculate with the muricatum- 

 group, but its ramifications in the Inferior Oolite are much more extensive. 



