318 
THE GEOLOGIST. 
justify the confusion of nomenclature whicli has hitlierto 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 difference of a fold or two in shells of this genus marks more 
than a diiference of age or of development ; 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 B. acuta first 
becomes known to us and those in wliich R. ajyiocejjhala disappears, 
specimens occur- 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 
teen 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 B. cynocephala 
to be identical — and Mr. Davidson has, I believe, adopted this view — 
with T. punctata, a shell which occurs in the marlstone associated 
with B. 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 trust 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 
similar nature. 
• R. rimosa and R. furcellata, also middle Lias shells, have been found in these 
beds by Dr. Wright, of Cheltenham, and myself. 
