90 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



83. Rhynchonella subconcinna, Dav. Plate XVII, fig. 17. 



Diagnosis. Shell more or less triangular, depressed, rather longer than wide ; valves 

 almost equally convex ; beak moderately produced, acute, nearly straight ; foramen almost 

 entirely surrounded by the deltidial plates, a small portion being completed by the umbo ; 

 beak ridges distinct, leaving a flat space between them and the hinge margin, which 

 indents that of the smaller valve. Surface ornamented by a great number of small plaits 

 from fifty to sixty on each valve ; the mesial fold and sinus are hardly perceptible, and 

 ornamented by from fourteen to fifteen plaits. Structure unpunctuated ; length 7, width 

 about 6, depth 3 lines. 



Obs. This species was found by Mr. Moore in the Marlstone of Ilminster, and seems 

 remarkable from the great number of minute striae which ornament its surface. It ap- 

 proaches in shape to some young shells of B. concinna ; but in these last, the costae are less 

 numerous and fine, nor does it ever appear to attain the same dimensions or character of 

 adult specimens of B. concinna. 



Fig. 17. From the collection of Mr. Moore. 



84. Rhynchonella obsoleta, Sow., Sp. Plate XVII, figs. 1 — 5. 



Terebkatula obsoleta, Sow. M. C, vol. i, 1812, p. 192, tab. lxxxiii, figs. 7, 8. 



— — Parkinson. 1822. An Introduction to the Study of Organic 



Remains, p. 234. 



— — Schlotheim. 1832. Syst. Vers, der Petrefacten. 



— concinna, Bronn. Leth. Geog., 1837, p. 289, pi. xviii, fig. 3, (non 



concinna, but obsoleta, Sow.) 



— obsoleta, Morris. Catalogue, 1843. 



— — Tennant. 1847. A Strat. List of British Fossils, p. 73. 



Diagnosis. Shell circular, or irregularly oval, gibbous, longer than wide ; beak acute, 

 produced, not much recurved ; foramen entirely surrounded by the deltidial plates, and 

 more or less separated from the umbo ; beak ridges distinct, leaving between them and 

 the hinge line a false area which indents considerably the smaller valve. Surface oramented 

 by from twenty-two to thirty-three strong acute plaits, five to eight of these forming a 

 slightly raised mesial fold with corresponding sinus in the other valve. Structure imper- 

 forated; length 19, width 17^, depth 13 lines. 



Obs. B. obsoleta was figured by Walcot, in 1799. 1 It occurs in the same localities 

 and beds as B. concinna, and is common to the Great Oolite of Hampton Cliff*, near 

 Bath, Felmersham, Cirencester, &c, nor is it rare in the Bradford Clay of Bradford, where 

 large specimens have been obtained, as may be seen from the fine series deposited in the 



1 Petrifactions found near Bath. 



