ON RHYNCHONELLA ACUTA AND ITS AFFINITIES. 5 



Yorkshire, it appears to me that the 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 

 Fossils," treats the difference of a plication, more or less, between 

 R. bidens and R. triplicata as unimportant, although, instead of 

 uniting these to It. acuta, and assigning to the three forms one specific 

 name, he records them as synonyms of R. variabilis, one of the most 

 widely-diffused brachiopods of the Lower Lias, and of which I doubt 

 the occurrence in the marlstone of England at least. 



In certain localities, as at Frocester, a young or dwarfed form of 

 It. tetrahedra constitutes the principal bulk of large masses of marl- 

 stone, 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 conse- 

 quence of having adopted, without due examination, his views. 

 Oppel, in his observations on R. variabilw (" Juraformation," p. 187), 

 after stating that it is found in the Middle as well as 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. bidens of Phillips), which is found also at the 

 base of the Middle Lias at Boll, Metzigen, Hinterweiler, 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 

 (p. 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. 



Professor Quenstedt, in like manner, in his recently-published 

 " Jura," treating of R. bidens, Phillips, seems disposed to consider it 

 and R. triplicata as varieties of R. acuta, distinctly pointing out their 



