ON HHTNCHONELLA ACUTA AND ITS AFFINITIES. 7 



Ripley in the Dogger, at Glaizedalo. I have little doubt that, had 

 Mr. Ripley's specimens been submitted to Cotteswoldian geologists, 

 they would have been named E. 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. acuia 

 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 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 justify the confusion of nomenclature which has hitherto 

 prevailed with regard to them. Why, then, should we make four, if 



