JONES — ON RHYNCHONELLA ACUTA AND ITS AFFINITIES. 315 



On comparing these witli the figures of R. acuta, R. bidens, and R. 

 triplicata, of Phillips, from the marlstone and ironstone-series of 

 Yorkshire, 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 

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

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

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

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

 ^videly-ditfused brachiopods of the Lower Lias, and of which I doubt 

 the occurrence in the marlstone of England, at least. 



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

 R. tetrahed7'a 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 views. Oppel, in 

 his observations onR. ^arm&2!Zis (" 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. 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 tha^ 

 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. 



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