212 SUPPLEMENT TO THE BRITISH 



Length 6, width 5^, depth 4 lines. 



Obs. — In 1852 I described two specimens of this small species as varieties of Rh. 

 variabilis, but having subsequently seen a number of German types, and a very good 

 series of figures by Quenstedt in pi. viii of his ' Der Jura,' I now perceive the necessity 

 of separating it from Schlotheim's species. I have figured two examples from a number 

 of British specimens from the Lower Lias of Stonehouse, which appear to correspond 

 exactly with some of Quenstedt's figured species. Our fig. 35 agrees with his fig. 19, 

 my fig. 36 with his fig. 17, and, indeed, I could have matched all his other figures 

 with British specimens. Therefore, I believe, we may consider the identity established. 



Many of the specimens seem also to approach Rh. oxynoti in shape ; and Rh. triplicata 

 juvenis is certainly related to that species. 



216. Rhynchonella varians, Schlotheim. Sup., PI. XXVIII, figs. 3 a, 3 b, 4, 12, 



and 13. 



Terebkatula varians, Schlotheim. Die Petrefactenkunde, p. 267, and for figure, 



Brugniere Encycl. Meth., pi. ecxli, figs. 5, 6', 

 1820. 



This species was not sufficiently described by Schlotheim, and the figure in the 

 ' Encyclopedic Methodique,' pi. ccxli, fig. 5 (fig. 12 of our Plate), to which he refers, 

 leaves some uncertainty with respect to its real characters. Schlotheim states that his 

 fossil was obtained at Amberg. 



In 1834, in his work ' Ueber Terebrateln,' pi. i, fig. 19, Baron von Buch gave a 

 profile view of what he considered to be the Tereb. varians, observing at the same time 

 that the shell is easily distinguishable from its congeners, above all by the manner in 

 which the smaller valve rises on leaving the hinge ; that the valve rises first by a gentle 

 curve, hardly perceptible, at an angle of 45°, to near the middle of the valve; it then rises 

 more abruptly, and afterwards, on approaching the front, becomes rapidly bent so as to 

 meet the serrated margin of the opposite valve. He added likewise that it occurs in the 

 upper portion of the Middle Jurassic formation of Germany, and that the bed containing 

 this fossil is rarely absent when one approaches the great white band which represents the 

 Upper Jurassic formation. 



Rh. varians, as we understand it, would form a group consisting, in England, of three 

 or four varieties, which, although differing but slightly, mark different geological horizons ; 

 so that without attaching any exaggerated importance to the varieties, which, although 

 useful in a certain sense as indicating distinct geological horizons, do not seem persistent, 

 I feel persuaded that the typical form of Rh. varians, as it is generally understood, has 

 continued to be represented from the Fullers' Earth up to the Lower Calcareous Grit, 



