146 GASTEROPODA OF THE INFERIOR OOLITE. 



perfectly reticulate pattern. The longitudinal ornament becomes slightly weaker 

 in the body-whorl. The upper row of spirals is rather more nodular and salient 

 than the others. Other indications wanting. 



Relations and Distribution. — This little shell seems to contain the germ of the 

 muricatum-group. It is met with sparingly in the Blue-Wyke Sand-rock, which 

 may be regarded as mainly in the opalinus-zone. 1 It is also quoted from the 

 jurensis-zone by Tate and Blake. 



The Muricatum-Group. 

 63. Oerithium muricatum, Sowerby, 1825 (Dogger variety). Plate VIII, figs. 2 a, 2b. 



1825. Tueuitella. mueicata, Sowerby. Min. Conch., vol. v, p. 159, pi. 499, 



figs. 1 and 2. 

 1829. — — — Phillips, Geol. Yorkshire, 1st ed., vol. i, 



p. 135, pi. iv, fig. 8. 

 1844. Cebithiumgbanulato-costatum, Munst. (pars). Goldf., Petrel'act. Germ., 



vol. iii, p. 32, pi. clxxiii, 

 fig. 10. 

 1884. — mueicatum, Sow. Hudleston Geol. Mag., dec. iii, vol. i, p. 51, 



pi. iii, figs. 1 and 2. 



Bibliography , Sfc. — Speaking in general terms C. muricatum, Sow., represents a 

 group rather than a species, nevertheless fig. 2 a is taken from one of Sowerby's 

 types. I have discussed this question at considerable length in the " Paleontology 

 of the Yorkshire Oolites" and will merely repeat my conclusions, viz. that in the 

 Yorkshire Dogger there are many varieties of Gerithia, such as those now figured 

 and others not figured, which are so plainly connected that they cannot be separated 

 specifically. Some of these, especially Sowerby's type, cannot be separated from 

 certain varieties in the Coralline Oolite of Pickering. 



Description. — Length 18 — 25 mm., spiral angle about 18°. Shell elongate, 

 strongly turrited ; whorls numerous, very slightly convex and rather constricted 

 anteriorly. Width of whorl to height as 5 : 3*5. Suture distinct ; ornaments con- 

 spicuous, consisting of granulated spiral bands usually four and sometimes five in 

 number, 2 which decussate with more or less numerous longitudinal ribs, which 

 latter usually have a slight inclination from left to right, and are sometimes slightly 

 arcuate. The nodes or spinous granulations at the points of intersection are 

 drawn out spirally, the upper band being somewhat the strongest. The body- 

 whorl is short relatively to the spire and similarly ornamented, but the spiral 



1 Ammonites of the section, Oxynoticeras, are most characteristic of the Blue-Wyke beds. 



2 The variety " sex-lineatwm " probably belongs to another species. 



