318 



THE GEOLOGIST. 



justify the confusion of nomenclature wliicli lias' hitherto prevailed 

 with regard to them. Why, then, should we make four, if not five, 

 species of that which is one only ? It is not pretended by naturalists 

 that the diiFerence of a fold or two in shells of this genus naarks more 

 than a difference of age or of deyelopment ; hence, assuming the 

 foregone conclusions to be correct, I venture to state that neither of the 

 forms noticed by the authorities cited, represents the full and perfectly 

 developed condition of this species. 



In a certain portion of the usually unfossiliferous sands near 

 Painswick, intermediate to those beds in which R. acuta first 

 becomes kno^vn to us and those in which R. cy^iocepliala disappears, 

 specimens occiir with the latter, by no means rare, which, on the 

 principles I have endeavoured to elucidate, must be referred to the 

 same species. These specimens not only attain to a much greater size, 

 but assume three or four mesial folds as their most common number. 

 I have not found them elsewhere, nor have I seen them in any other 

 collection than my own ; but this happens probably from their having 

 been considered unworthy of retention, on account of the imperfect 

 state in which they are usually found. 



I would remark, in conclusion, as lending additional force to my 

 observations, that Mr. Hull considers the Terebratula which occurs so 

 abundantly in the Frocester and Haresfield beds* with R. cynoceijliala 

 to be identical — and Mr. Davidson has, I believe, adopted this view — 

 with T. punctata, a shell which occurs in the marlstone associated 

 with R. acuta; we cannot, therefore, be surprised, from their manifest 

 community of habit, that these two species should have gone through 

 time together, from the period of their first creation to that of their 

 final extinction. 



I tru.st that these observations on the natural history of an extinct 

 Brachiopod may not have seemed tedious: but I believe every true 

 geologist will appreciate any endeavours to clear up errors or con- 

 fusion, however small, with regard to any of his " time and tide " 

 marks ; while the possible demonstration of the wide divergence of 

 varieties from their assumed types, as exemplified in this ancient 

 species under varied conditions of existence, may not be devoid of 

 interest to the physiologist in his investigation of phenomena of a 

 s'milar nature. 



* R. rimosa and R. furcellata, also middle Lias shells, have been found in these 

 beds by Dr. Wright, of Cheltenham, and myself. 



