JONES — ON RHYNCHONELLA ACUTA AND ITS AFFINITIES. 317 
In Phillips's " Geology of Yorksliire," this marlstoiie shell, there 
first figured and described, is stated, at page 157, in the list of organic 
remains of the Inferior Oolite, to have been found by Mr. Eipley in the 
Dogger, at Glaizedale. I have little doubt that, had Mr. Ripley's 
specunens been submitted to Cotteswoldian geologists, they would have 
been named R. cynoeephala, and the close resemblance of certain forms 
of this shell to the former, which induced a practised observer to 
consider both specifically identical, suggests the expediency of inquirmg 
whether they may not really be so. 
Mr. Lycett finds R. cynoeephala in the marly beds lying at the base 
of the sands which, in this district, usually rest upon the upper Lias, as 
at NaUsworth and elsewhere, although it has long been considered 
peculiar to the "Cephalopoda-bed" above those sands. It abounds at 
the Horsepools, Haresfield, and Frocester, where it presents three 
similar degrees of variety, attained to by those R. acuta in the 
Inarlstone. From the thin ferruginous earthy band dividing, at 
Haresfield, the "Cephalopoda-bed," into two portions, they are most 
readily extracted ; the specimens are all more or less stunted in growth 
as compared with those from above or below ; and there j^rincipally I 
have found the acute variety. The only recognizable feature of dis- 
tinction betAveen this and R. acuta is, that in the former the apex is 
not so much elevated, and is formed by a less acute angle than in the 
latter, approximating more nearly to its younger forms ; although this 
difference of outline may partly be accounted for, by the fact that the 
marlstone, in the one case, only affords us casts, through the intractable 
nature of the matrix, while, in the other, the shells are exceedingly 
well preserved, exhibiting clearly lines of groAvth and perfect details 
of the states of mattirity at which they had arrived. 
With so great a constancy of form to a limited set of specific types 
as to perplex us, and to render essential the considerations of strati- 
graphical position in separating them, and with these derived from 
beds almost immediately following each other, it is not clear that 
valid grounds exist for their separation. All these forms indisputably 
have the same vertical range ; they differ in no greater degree from each 
other than do the varieties of other universally acknowledged species. 
They appear and disappear simultaneously in strata of which they are 
everywhere some of the most remarkable fossils, and in which they 
are not associated Avith others that rcscml^lc them so much as to 
