RHYNCHONELLA. 89 



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



— — Bronn, 1848. Index Palseont., p. 1233. 



Rhynchonella concinna, If Orb. Prodrome, vol. i, p. 315, 1849. 



Diagnosis. Shell inequivalved, when adult nearly gibbose, more or less compressed, 

 in the young; rather wider than long, beak acute and slightly recurved, foramen not 

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

 umbo, especially so when young, and up to a certain age in the adult state; the two plates 

 sometimes meeting at the umbo. Beak ridges well defined, leaving between them and the 

 hinge-line a false area, not much indenting the smaller one ; surface ornamented by a 

 variable number of acute plaits, about thirty-two in each valve, seven to eight of which 

 forming a slightly elevated mesial fold, corresponding to a sinus in larger valve ; structure 

 imperforated. Length 11, width 12, depth 10 lines. 



Obs. This is one of the oldest described species in the ' Min. Con.,' it is abundant 

 in the Great Oolite of many localities in England, and is found at Hampton Cliff, Aynhoe, 

 near Bath, Cirencester, &c. At Bradford it is found in the Bradford clay, and is one of 

 our most common British and foreign species. 



R. concinna is flat and compressed, when young, with hardly any visible mesial fold, 

 {T.flabellula, Sowerby,) becoming convex and gibbose with age. Ter. rostrata 1 of that 

 author, belongs likewise to this species, and is only a specimen where the beak is un- 

 usually elongated, of which any one will be convinced on inspecting the original spe- 

 cimens in the collection of Mr. J. de C. Sowerby ; nor is it a Cretaceous shell, as 

 stated by that author. M. D'Orbigny 2 is mistaken when mentioning Ter. obsoleta, 

 Sowerby, as only a young state of concinna, an error at once evident from the last 

 being a much smaller shell, and is distinguished from obsoleta by several characters 

 alluded to under the head of that species. 3 



Plate XVII, fig. 6, illustrates an adult example from Cirencester. 



„ figs. 7, 8. Middle aged specimens, likewise from Cirencester.* 



,, figs. 9, 10. Young individuals, Ter.fiabellala, of Mr. Sowerby. 



,, fig. 11. An exceptional specimen, T.rostrata, of Sowerby. 



,, fig. 12. An enlarged illustration of the beak and foramen. 



1 In Mr. Sowerby's figure, the foramen is incorrectly placed. 



2 Prodrome, vol. i, p. 315. 



3 In a paper lately published, (Mem. de la Soc. Geol. de France, vol. iv, 2d ser., p. 28, pi. viii, figs. 10, 

 11, 1851,) Mr. Bayle describes and figures as T. concinna, Sowerby, a shell winch does not seem to me to 

 belong to that species, but more like R. lacunosa, Schlotheim, nor does the figure 10 of the same author 

 appear referable to R. lacunosa. 



4 The recent Rh. nigricans, Sow., Zool. Proc, 184G, is undistinguishable from half grown R. concinna, 

 Sow., the former of which was dredged by Mr. Evans, R.N., in 19 fathoms, Foveaux Strait, New Zealand, 

 about five miles north-east of Ruapuke Island, examples of which may be seen in the collections of 

 Messrs. Evans, Cuming, and the British Museum, but probably never becomes as globular, as that species 

 is fouud, when adult. 



