CERITHIUM. 153 



related to CerUhium costellatum, Miinst. (non Deslong.), as that fossil occurs 

 in the Upper Lias of Compton, and some of the Bradford-Abbas specimens 

 are scarcely to be distinguished from the Lias species, where, however, the costae 

 are somewhat straighter — a very unimportant difference. Taken as a whole, with 

 all its varieties, this species is eminently characteristic of the Lower Division of 

 the Inferior Oolite, but seldom so well preserved or of such large size as in 

 Dorsetshire. Though the ornameuts are considerably modified by conditions of 

 preservation, it may be recognised in a granulato-costate condition in other places, 

 as, for instance, in B of Mr. Walford's Hook Norton section. CerUhium vetustum- 

 majus of the Dogger is probably its local representative in the Yorkshire-beds. 



69. Cerithium subscalariformk, D'Orb., variety in the Humphriesianus-zone. 



Plate VIII, fig. 9. 



This form is very near to G. subscalariforme as it occurs in the beds of 

 Bayeux; it is somewhat smaller, and in the figured specimen the body-whorl 

 appears unusually short. The costse also happen to be somewhat more granular 

 as in granulato-costatum, Miinst. Occurs in the Sauzei-bed at Oborne. 



70. Cerithium subscalariforme, D'Orb., variety in the Parkinsoni-zone. Plate 



VIII, figs. 10 a, 10 b. 



Cf. Melania tjndulata, var. a, Deslongchamps, vol. cit., p. 217, pi. xi, fig. 58. 



Description. — As compared with the previous variety, or varietal group, there can 

 be no better description than "testa breviori; costis et striis crassioribus rariori- 

 busque." This is a much shorter form, it is more widely angled, and when in the 

 granulato-costate condition the spirals are not usually more than four or sometimes, 

 in well-developed specimens, five. Corresponding to the greater width of the shell 

 the aperture is widely ovate, and it so happens that in the majority of the available 

 specimens the anterior canal is by no means distinct (probably the result of wear). 



Relations and Distribution. — This variety possibly represents rather than 

 resembles the C. vetustum of the Yorkshire-beds. It is essentially a fossil of the 

 Upper Division, and is moderately common. The specimen from Grove (fig. 10 a) 

 greatly resembles the figure in Deslongchamps' work (xi, 58), and is exceptionally 

 fine. Away from the Dorset-beds the specimens become poorer, worse preserved, 

 and maybe variously described as C. granulato-costatum, G. muricato-costatum, and 

 even G. vetustum according to local circumstances. 



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