ON RHYNCHONELLA ACUTA AND IS AFFINITIES. 7 
Ripley in the Dogger, at Glaizedale. I have little doubt that, had 
Mr. Ripley’s specimens been submitted to Cotteswoldian geologists, 
they would have been named R. cynocephala, 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 ex- 
pediency of inquiring whether they may not really be so. 
Mr. Lycett finds R. cynocephala in the marly beds lying at the 
base of the sands which, in this district, usually rest upon the upper 
Lias, as at Nailsworth and elsewhere, although it has long been con- 
sidered peculiar to the “Cephalopoda-bed” above those sands. It 
abounds at the Horsepools, Haresfield, and Frocester, where it pre- 
sents three similar degrees of variety, attained to by those R. acuta 
in the marlstone. 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 
principally I have found the acute variety. The only recognizable 
feature of distinction between 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 
growth and perfect details of the states of maturity 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 followimg 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 with others that resemble them so 
much as to justify the confusion of nomenclature which has hitherto 
prevailed with regard to them. Why, then, should we make four, if 
