CERITHIUM. 145 



canal almost effete, a feature always accentuated by wear. But the connection of 

 these forms with others, where the anterior canal is fairly well developed, is so 

 obvious that we cannot fail to place them under Cerithium. 



It must be borne in mind that mineralization has, in many cases, so affected 

 the ornaments of Cerithia, especially of those preserved in calcareous rocks, as to 

 produce more confusion than in any other class of shells. When to this is added the 

 sporting or variation of an abundant group, the difficulties of nomenclature become 

 very serious. For these reasons the common or demoid forms have given rise to 

 more names than may be absolutely necessary. There are two of these demoid 

 groups of Cerithium which more or less pervade the Oolites, at least as high as 

 the Corallian-rocks. These are the muricatum-group, including the quondam 

 " Chemnitzia " vetusta and its allies, and the limceforme-group. An attempt has been 

 made to arrange the several species in something like the order of their apparent 

 relationship. The last group included under Cerithium comprises four species, 

 which might almost be constituted into a subgenus, if indeed they are not allied to 

 one already constituted. Externally the species of this group have considerable 

 resemblance to Nerincea, but their internal structure is quite different. 



As regards the possible origin of the Cerithia of the Inferior Oolite, we may 

 suppose that some of them are the modified descendants of species occurring in 

 the Lias. The intermediate sands, whether belonging to the opalinus-zone or to 

 the jurensis-zone, seem to oppose a barrier, usually not very fossiliferous, between 

 the abundant fauna of the bifrons-beds, and the more calcareous beds of the 

 Inferior Oolite. Some small Liassic species, such as Cerithium armatum, C. 

 quadrilineatum, and Cryptaulax scobina, still linger in the lower part of these sands. 

 Somewhere in the opalinus-zone, as is well exemplified in the Yorkshire Dogger, 

 Cerithia became both larger and more plentiful, whilst the fauna of the Inferior 

 Oolite now presents itself to the collector in abundance. 



62. Cerithium quadrilineatum, Bomer, 1836. Plate VIII, fig. 1. 



1836. Turritella quadrilineata, Bomer. Ool. Geb., p. 154. 



1850. Cerithium quadrilineatum, B'Orh. Prod., i, 250, Etage Toarcien. 



1869. — — Bomer. Brauns, Mitt). Jura, p. 171, pi. ii, 



figs. 7 and 8. 

 1876 Tate and Blake, York. Lias, p. 351. 



Description of a Dogger Specimen. — Length 6 mm., width 2 mm. Shell elongate, 

 subturrited. The spiral angle is regular ; whorls seven or eight, nearly flat, well- 

 divided by the suture. The ornaments consist of from four to five spirals, which 

 reticulate with slightly arcuate longitudinals of about equal strength, producing a 



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