JONES — ON RHYNCHONELLA ACUTA AND ITS AFFINITIES. 817 



In Phillips's " Gteology of Yorksliire," this niaiistone 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. Kipley in the 

 Dogger, at Glaizedale. I have little doubt that, had Mr. Eipley's 

 specimens been submitted to Cotteswoldian geologists, they would have 

 been named R. cynocejjhala, and the close resemblance of certain forms 

 of this shell to the former, which induced a practised observer to 

 C3nsiderboth specifically identical, suggests the expediency 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 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 

 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 dis- 

 tinction 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 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 with others that resemble them so much as- to 



