96 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



there ; at one time, I thought they might belong to T. helvetica, Schloth., but that species 

 is so badly characterised, as well as figured, that it would be unsafe to refer our shell to 

 that form; neither Schlotheim's nor Zieten's figure apparently possessing any definite mesial 

 fold. I have, therefore, under these circumstances, given it a distinct appellation. 



II. subtetraedra is found in the Inferior Oolite of Dundry and Leckhampton Hill, near 

 Cheltenham, where it has been collected by Mr. Walton and Dr. Wright. 



Plate XVI, fig. 12. A variation with hardly any distinct mesial fold and few plaits, 



from the Inferior Oolite of Somersetshire, in the collection of 

 the Geological Survey. 

 ,, fig. 9. A large specimen from the Inferior Oolite, Dundry. 



fig. 10. A specimen from Dundry, in the collection of Mr. Walton, 

 fig. 11. A variety from the Upper Ferruginous Bed of Leckhampton Hill, 

 in the collection of Dr. Wright. 



90. Rhynchonella lacunosa, Schloth., Sp. Plate XVI, figs. 13, 14. 



Terebratulites lacunosa, Schlotheim. 1813. Beitrage fur Nat. Vers., in Leonhard's 



Min. Tasch., vol. vii, pi. i, fig. 2. 

 Terebratula lacunosa, V. Buck. 1834. Uber Ter.; and 1838, Mem. Soc. Geol. de 



France, vol. iii, first ser., p. 150, pi. xv, fig. 22. 

 _ _ Bronn. Index Pal., p. 1239, 1848. 



Rhynchonella lacunosa, VOrb. Prodrome, vol. i, p. 375, 1849. 



Diagnosis. Shell irregularly, transversely oval, wider than long ; beak acute, recurved ; 

 foramen entirely surrounded by the deltidium, but lying close upon the umbo ; the false 

 area between the beak ridges and hinge margin is well defined, a similar depression existing 

 likewise on either side of the umbo ; valves unequally convex, and ornamented by a variable 

 number of plaits, from eighteen to nineteen on each valve, four, five, or six forming a pro- 

 duced elevated mesial fold, to which corresponds a deep sinus in the other valve ; the 

 convexity of the valve seems regular from the umbo to the front, the deepest portion of the 

 shell being towards its centre; length 12, width 13, depth 9 lines. 



Obs. The specimens described above were obtained by Mr. Robertson, of Elgin, at 

 Dunrobin, in Scotland, in beds referred to the Oxford Clay ; and on comparing the well- 

 preserved specimens forwarded by that gentleman with Schlotheim's figures of T. lacunosa, 

 (1813,) I am disposed to believe them referable to the same species, which is peculiar to 

 the Upper Jura on the Continent, and placed by M. D'Orbigny both in his Terrain 

 Oxfordien and Callovien. It is, however, no easy matter to come to a certain conclusion 

 on several species of Rhynchonella, for two principal reasons, the first, arising from the 

 extreme variability of the shells of some species of this genus, and especially on account of 

 the insufficient manner in which most authors have determined, figured, or described 

 their species. In the case before us, it would be a waste of time to attempt a 



