RHYNCHONELLA. 95 



In England, B. tetraedra is found in the Upper and Middle Lias or Marlstone of many 

 localities ; it abounds in the neighbourhood of Ilminster, where it attains very large 

 dimensions, as maybe remarked from the figures, PL XVIII, figs. 6 and 7. It is likewise 

 plentiful, but smaller, in the Lias of Radstock, Deddington in Yorkshire, &c. Mr. Sowerby 

 mentions Aynhoe and Banbury in Oxfordshire, Von Buch states the species to occur in 

 the Inferior Oolite of Dundry, 1 whence, however, I have not seen any authenticated 

 specimens. Mr. Morris 2 mentions it from the Inferior Oolite of Somerset, from the 

 Kelloway Rock of Kelloway, and from the Puller's Earth, Banbury ; but in the multitude of 

 specimens sent me from all those formations of the Oolitic period, I have never been so 

 fortunate as to recognise any authentic specimen of the species, except one remarkable 

 example, PL XVIII, fig. 10, sent me by Mr. Walton, and said to be from the Inferior 

 Oolite of Leckhampton Hill, Cheltenham, which approaches likewise to some varieties of 

 B. decorata. On the Continent the species is found in many localities ; at Landes, Evreci, 

 Fontaine-Etoupefour, &c, in Normandy, also in Germany. 3 



Plate XVIII, fig. 5. A type specimen, in the collection of Mr. J. de C. Sowerby. 

 „ figs. 6, 7. From specimens in the collection of Mr. Moore. 



,, fig. 10. From the Inferior Oolite of Cheltenham, in the collection of 



Mr. Walton. 



89. Rhynchonella subtetraedra, Dav. Plate XVI, figs. 9 — 12. 



Diagnosis. Shell more or less transversely circular, generally wider than long ; valves 

 nearly equally convex, rarely gibbous, somewhat compressed ; beak acute, moderately pro- 

 duced, and slightly recurved; foramen of moderate size, entirely surrounded by the 

 deltidium ; a narrow flat or slightly concave false area existing between the beak ridges 

 and hinge margin which does not indent much the smaller valve. Surface ornamented by 

 a variable number of acute plaits, from twenty to thirty on each valve ; mesial fold more or 

 less produced, composed of a variable number of plaits in general from five to nine ; 

 sinus shallow, dimensions variable; length of largest specimen 21, width 24, depth 

 14 lines. 



Obs. On comparing the shells under notice with a number of known species, I have 

 not been able to identify them with any of the described types; they vary from concin/ia 

 and obsoleta, being much more transverse and strongly plaited ; from tetraedra they likewise 

 differ sufficiently not to represent that type. With lacunosa they have some resemblance, 

 but on comparing our form with that shell, I could not make up my mind to place them 



1 Mem. Soc. Gcol. de France, vol. iii, p. 140. 



2 Catalogue of British Fossils, 1843. 



3 Messrs. Bayle and Coquand, figure and describe a Rhynchonella from the Lias of Mannas, Chili, as 

 belonging to T. tetraedra, Mem. Soc. Gcol. de France, vol.iv, 2de ser., p. 17, 1851 ; but I cannot recognise 

 the true type of the Sowerby species in their figure. 







