JURASSIC AND TRIASSIC BRACHIOPODA. 195 



Some specimens were proportionately less deep. In general shape they varied also 

 considerably, some being almost globose and transversely oval, and others more or less 

 pentagonal. Some were perfectly symmetrical, the mesial fold broad, distinct, well 

 marked, and situated in the middle of the valve, while in others it is twisted to one or the 

 other side, the shell then becoming unsyrametrical, as in Rh. inconstans. This character 

 is, however, observable in many other species of the genus, not only in the Jurassic, but 

 also in the Cretaceous (Rh. contorta), Tertiary, and even recent periods. I have examples 

 of the living Rh. nigricans in which the fold and sinus are shifted to one or the other side 

 of the valves. In the variety under description, the number of angular ribs in each valve 

 varies from twenty to twenty-eight, and of this number from five to eight occupy the fold 

 or sinus ; the beak is moderately large and incurved, with a small circular foramen under 

 its angular extremity. 



It seems to me that Rh. pectunculoides, Et., Rh. semiconstans, Et., and Rh. pullirostris, 

 E.t, are all referable to a single species, that is, if we are to judge from the figures in the 

 ' Lethaea Bruntrutana.' Some specimens from Abbotsbury correspond with all Thurmann 

 and Etalon's figures. 



At p. 242 of his work on the Boulonnais, already referred to, M. de Loriol observes 

 that " The Rhynchonellce from the Upper Jurassic deposits belonging, to the Rh. pinguis 

 group, are so difficult to distinguish correctly that several authors have referred them to a 

 single species. Thus, M. Cotteau combines all the Rhynchonella from the Upper 

 Jurassic deposits of the Department of the Yonne under the designation of Rh. inconstans. 

 Dollfus does likewise with those of Havre, while Dr. Brauns recognises only the Rh. 

 pinguis in the Upper Jurassic deposits of Hanover. That author observes that " Rh. 

 inconstans (at least as it is understood by Mr. Davidson), is distinguishable by its shorter 

 and more incurved beak and its less acuminated area ; the specimen from the Coral 

 Rag figured by Mr. Damon under the name of Rh. obsoleta, Sow., corresponds exactly 

 with our individuals from Boulogne." 



Mr. J. F. Walker proposed to me to distinguish the Abbotsbury form by the 

 varietal designation of Supra-corattina, but I think that one of Etalon's names should be 

 adopted in preference to a new one. M. de Loriol 's figures of Rh. pectunculoides 

 (Haute-Marne, PI. XXVI, figs. 1 — 3) correspond exactly with many of the specimens from 

 Abbotsbury. By far the larger number of the specimens from the last-named locality 

 occur in the shape of internal casts, but examples with the shell preserved are occasion- 

 ally obtained. 



