JONES — ON RHYNCHONELLA ACUTA AND ITS AFFINITIES, 315 
On comparing tliese with the figures of R. acuta, R. hidens, and R. 
triplicata, of Phillips, from the marlstone and ironstone-series of 
Yorkshu'e, it appears to me that that author has merely represented 
more aged examples of the two varieties before us as species distinct 
from the first-named. 
Professor Morris, in the last edition of his " Catalogue of British 
FossUs," treats the difference of a plication, more or less, between 
R. hidens and R. ivlplicata as imimj^ortant, although, instead of 
imiting these to R. acuta, and assig-ning to the thi'ee forms one specific 
name, he records them as synonj-ms of R. variahilis, one of the most 
widely-diffused brachiopods of the Lower Lias, and of which I doubt 
the occiirrence in the marlstone of England, at least. 
In certain localities, as at Frocester, a young or dwarfed form of 
R. tetrahedra constitutes the principal bulk of large masses of marlstone, 
and has, I think, been mistaken for R. variabilis; but in neither 
of these species can I discover any features at all suggestive of affinity 
■with that under consideration. That Professor Morris may be mis- 
taken is not improbable, from the fact that the two most recent writers 
on the Jurassic formations of England and the continent, Oppel and 
Quenstedt, have both found themselves somewhat perplexed as to the 
true affinities of these forms, perhaps, to some extent, in consequence 
of having adopted, without due examination, his Aaews. Oppel, in 
his observations on i2. m?■^a&^7js (" Juraformation," p. 187), after stating 
that it is found in the Middle as well as in the Lower Lias, remarks, 
pertinently enough as regards the object of the present paper, that, " in 
Suabia it occurs particularly under the form of the biplicated variety 
{R. bidena of Phillips), which is found also at the base of the Middle 
Lias at Boll, Metzigeu, HinterweUer, and Balingen, with specimens 
possessing a greater number of folds {R. variabilis of Zieten, p. 42, 
f. 6, and R. triplicata of Phillips.) 
Bearing in mind the fact that R. variabilis of Zieten is not the 
typical form recognized by Schlotheim or Davidson, it is clear that 
Dr. Oppel considers the forms just described as belonging to one 
species, and, in his observations on R. variabilis of the Lower Lias 
121), he appears disposed to limit its stratigraphical range to the 
Lower Lias only, in which case, of course, they are not varieties of the 
latter. 
2 B 2 
