TEREBRATELLA. 25 



Teuebratula Menardi, V. Buck. 1834. Uber Ter., and Mem. de la Soc. Geol. de 



France, vol. hi, p. 184, pi. xvii, fig. 6, 1838. 



— — Deshayes. Nouv. Ed. de Lamarck, vol. ii, p. 344, No. 50, 



1836. 



— truncata, Sow. Min. Con., vol. vi, p. 71, tab. 537, fig. 3, 1829. 



— Morris. Catalogue, p. 137, 1843. 



— — Forbes. Quart. Journ. of the Geol. Soc, p. 346, No. 105, 



1845. 



— — Tennant. A Strat. List of British Fossils, p. 47, 1847. 

 Tekebratella Menardi, D'Orb. Pal. Franc. Ter. Cretacees, vol. iv, p. 118, pi. 517, 



figs. 1—15 (not T. Astieriana, D'Orb.), 1847. 

 Terebratula — Bronn. Index Pal., p. 1241, 1848. 



— truncata, Austen. Quart. Journ. of the Geol. Soc, vol. vi, p. 477, 



1850. 



— Menardi, Cunnington. Quart. Journ. of the Geol. Soc, vol. vi, p. 454, 



1850. 

 Terebratella — D'Orb. Prodrome, vol. ii, p. 172, 1850. 



Terebratula — Gue'ranger. Bull, de la Soc. Geol. de France, vol. vii, 



2d ser., p. 803, 1850. 



Diagnosis. Shell semicircular, generally transverse, as wide, or wider, than long ; 

 rarely longer than wide ; hinge-line forming a very obtuse angle, sometimes nearly straight, 

 and almost as wide as the shell ; larger or dental valve most convex, with a longitudinal 

 sinus, extending from the beak to the front; beak large, straight, presenting a well 

 defined, oblique, triangular area, truncated by a large foramen, and completed by 

 two indented deltideal plates, which separate it more or less from the umbo ; smaller 

 valve less convex than the dental one, with a well-defined mesial fold extending from 

 the umbo to the front, and producing an elevated curve ; surface of valves ornamented 

 by a variable number of sharp plaits, rarely bifurcating, but more commonly augmenting 

 by the intercalation of other costae at different distances from the umbo and beak. From 

 eighteen to thirty plaits may be counted on each valve, according to age ; from six to seven 

 ornamenting the mesial fold and sinus; these longitudinal plaits are more or less intersected 

 by concentric wrinkled lines of growth, often so close as to give the costae a somewhat 

 granulated appearance. Structure punctuated ; in the interior of smaller valve the boss is 

 much produced, on either side of which two deep condyles are seen to receive the articu- 

 lating teeth of the dental valve ; the loop is doubly attached ; a slightly elevated longi- 

 tudinal ridge is visible in the interior of larger valve, extending to about half the length 

 of the shell ; dimensions variable : length 6£, width 7, depth 4 lines. 



Obs. Professor Forbes, Bronn, Morris, and others have long considered the Ter. 

 truncata, Sow., as a synonym of T. Menardi, Lamarck, an opinion in which I quite coincide, 

 from having compared with great care many specimens of our British shell with those from 

 France, and collected by myself in both locahties. M. D'Orbigny, however, believes that 

 our views are erroneous, and I suppose without having been able to examine a series of 



