W. H. Hudleston—The Yorkshire Oolite. 485 
the base, so as to accentuate the suture, but in the majority of cases 
this feature is less obvious. 
Though apparently without ornament, closer examination reveals 
a very fine transverse striation (Fig. 6b), which varies according to 
the accidents of preservation. In this specimen it is seen only on 
the lower whorls, but in some specimens may be observed to extend 
much further up the spire. Aperture involved in matrix. 
Fig. 6c. Another specimen from the Coral Rag of Brompton (my 
Collection). 
The dimensions are proportionate to those of the preceding speci- 
men, but the sutures are much less deep owing to wear, and all traces 
of the fine striation are lost. The Cerithium-like character of the 
aperture is well shown. In this condition the shell is very com- 
mon in the Coral Rag of Brompton. 
Relations and Distribution—The very plainness of this shell is 
against instituting a comparison with others. The Yorkshire shell 
is very abundant in the Coral Rag of the Scarborough district, which 
includes Seamer, Ayton, and Brompton, but not at all common else- 
where. It is just possible that there may be two species of unorna- 
mented Cerithia in these beds. 
Genus Nextnma, Defrance, 1825. 
There are few genera so difficult to arrange and describe satisfac- 
torily as the Nerinzas of the Yorkshire Corallian beds. In some 
measure this is owing to the rolled and fragmentary condition of the 
shells and also to a sort of action which seems to have absorbed 
and destroyed the ornamentation. In the second edition (18385) of 
Phillips’s Geology of Yorkshire, there is no mention of any example 
from the Corallian beds; and in the third edition (1875) only two 
species are quoted in the table at page 258. 
There is great poverty in this respect in some of our museums and 
private collections; and yet the genus, as regards numbers of in- 
dividuals, if not of species, is well represented throughout the cal- 
careous beds of the Corallian series. Hven the Lower Limestones, 
so poor in Gasteropoda, contain narrow, cylindrical species, having an 
outline similar to N. Remeri; and when we come to the Upper 
Limestones we find Nerinzas very numerous, especially in the 
Coralline Oolite, but they are difficult to extract, so as to show any 
character. 
Much caution is required in attempting to name or describe frag- 
ments belonging to this genus; for we must bear in mind, as 
Buvignier has well pointed out, that the spiral angle often differs 
considerably in the same species. In some the exterior form under- 
goes modifications with age; so also it is with the form and dispo- 
sition of the interior folds, which even vary in number. For this 
reason detached portions really belonging to the same species may 
receive different names, and this danger is especially to be guarded 
against in our beds, where entire shells, showing ornaments, are so 
difficult to procure. In addition to the forms which I have selected 
for figuring, there are one or two others which cannot be referred to 
