148 GASTEROPODA OF THE INFERIOR OOLITE. 



The numerous varieties and species which I refer to the vetustum-grouip 

 have a tendency to longitudinal ornament, and even when their ornaments 

 are markedly granular, the granules are usually drawn out axially rather 

 than spirally. Cerithium Jiexuosum, Munst., as it seems to me, represents the 

 immature condition of some varieties, where arcuate longitudinal costae prevail 

 before any turriting has commenced, whilst C. muricato-costatum represents 

 robust varieties, where the granules have been more or less fused into continuous 

 longitudinal costae. This tendency to longitudinal ornamentation, so conspicuous 

 in corroded specimens, has caused the original Terebra vetusta of Phillips to be 

 classed under " Chemnitzia" even by D'Orbigny, although the representative 

 species in the Bajocian of Normandy (Nos. 172 and 188 of the 10th stage) are 

 classed under Cerithium in the ' Prodrome.' 



As regards nomenclature, the difficulties which beset all demoid forms are 

 aggravated in this case. Firstly, the prior name was given to a corroded specimen 

 of the stunted species which occurs in the Millepore- and Scarborough-Limestone. 

 Secondly, the whole group is peculiarly liable to have its ornaments affected by 

 variations in conditions of mineralization, and this is particularly the case in the 

 beds whence the type was derived. Minister's names, though very useful, and no 

 doubt applicable to the German beds, represent conditions of mineralization, and 

 in the case of C. fiexuosum (only 10 mm. in length) even a stage of growth in all 

 probability. Without in any way asserting, that the method adopted in this Mono- 

 graph for dealing with such an extensive group is the best, it possesses the merit 

 of exhibiting the facts of the case as they occur in the Inferior Oolite of this 

 country. Some dubious forms, presumably belonging to this group, have not been 

 noticed, but Miinster's names would cover the majority of them. 



65. Cerithium vetustum, Phillips, 1829. Plate VIII, figs. 5 a, 5 b, 5 c, 5 d. 



1829. Tebebba vetusta, Phil. Geol. York., Pt. I, vol. i, p. 152, pi. ix, fig. 27. 



1844. Ceeithium muricato-costatum, Munst. Goldfuss, t. 173, fig. 12. 

 1844. — geanulato-costatum, Munst. Goldfuss, t. 173, fig. 10. 



1844. — ? flexuosum, Munst. Goldfuss, t. 173, fig. 15. 



1850. Chemnitzia vetusta, If Orb. {Phil.). Prod., vol. i, p. 263. 



1851. — ? — Phil. Morris and Lycett, p. 114, pi. xv, fig. 7. 

 1869. Cebithium vetustum, Williamson. Brauns, Mittl. Jura, p. 172. 



1882. " Chemnitzia " vetusta, Phil. Hudleston, Geol. Mag., dec. ii, vol. ix, 



p. 247, pi. vi, figs. 9—11. 



Bibliography, 8fc. — Brauns, in sweeping up the muricato- and granulato- 

 costate Cerithia of North-west Germany into this net, included Cerithium armatum, 



