84 BRITISH OOLITIC AND LI ASIC BRACHIOPODA. 



nut, wider than long ; valves convex ; beak acute, small, more or less recurved ; foramen 

 circular, always lying close to the umbo, being entirely or partially surrounded by the 

 deltidial plates, a small portion of the circumference being completed by the umbo, a 

 flatness or false area existing between the beak ridges and the hinge margin, which last 

 does not much indent the smaller valve. Surface ornamented by a variable number of 

 small plaits, about twenty-four on each valve, from five to six, or seven, rarely three, 

 forming an elevated mesial fold, the smaller valve arising from the umbo, by a gentle curve 

 to about half its length, when the inclination becomes more rapid as it approaches the 

 extremity of the valve where it is suddenly bent downwards to meet a well-defined and 

 deep sinus ; the plaits in the sinus seems, as if longitudinally depressed or split in their 

 centre, as they approach the front margin. Structure imperforated ; length 8, width 7^, 

 depth 5 lines. 



Obs. This variable shell received, in 1820, from Schlotheim, the name of varians, 

 that author referring to the very indifferent figure in the c Ency. Meth.' unnoticed by 

 Sowerby, it was subsequently figured by Professor Phillips, under the name of Ter. socialis, 

 which name has been admitted by Mr. Morris and Prof. Bronn to be a synonym, of which I 

 convinced myself by comparing the Professor's shell kindly lent me by Mr. Bean, with the 

 German types. It was well described by Baron Von Buch, who states it to occur by 

 millions where it is found. In England, it is abundant in the Fuller s Earth round Bath, 

 also at Scarborough and Hackness, and in the Kelloway Bock of Kelloway, from which 

 locality I am indebted to Mr. Walton for many examples. On the Continent, it is stated 

 by Von Buch to occur in the upper portions of the Middle Jura, it is rarely wanting in the 

 bed approximating to the Upper Jura, at Beggingen and at Osterfingen, in the canton 

 of Schaffouse, at Fiirstenberg, near Bahlingen, in the Wurtemberg, near Doneschingen, 

 near Amberg, &c. 



The Terebratula figured by Zieten, under the name of Ter. varians, does not 

 belong to the species, as correctly remarked by M. D'Orbigny; it more resembles 

 R. cynocephala, (Rich.) ; B. varians of Schlotheim, is placed by M. D'Orbigny in his 

 {Ter. Oxfordien.) 



Figs. 15, 16. Two specimens, nat. size. 



Fig. lb hci . Enlarged illustrations. 



78. Rhynchonella Forbesii, Dav. Plate XVII, fig. 19. 



Diagnosis. Shell inequivalve, globular, and circular, beak small, recurved, foramen 

 entirely surrounded by the deltidium; hinge margin of larger valve not much indenting that 

 of the smaller; surface ornamented by about twenty small plaits on each valve, five or six of 

 which form a raised mesial fold not projecting distinctly above the lateral plaits: the sinus 

 is very shallow. Length 4, breadth 3£, depth 3 lines. 



