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 Cerithiwm. 
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 Cerithiwm 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 limeforme-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 Cerithiwm 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 Nerinea, 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 Oryptaulae 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, Rémer, 1836. Plate VIII, fig. 1. 
1836. TURRITELLA QUADRILINEATA, Romer. Ool. Geb., p. 154. 
1850. Crrrrnium gvaprininnatum, D’Orb. Prod., i, 250, Etage Toarcien. 
1869. — — Romer. Brauns, Mittl. Jura, p. 171, pl. ii, 
figs. 7 and 8. 
1876 — — Tate and Blake, York. Lias, p. 351. 
Description of a Dogger Specimen.—Length 6mm., width 2mm. 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 
19 
