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SUPPLEMENT TO THE BRITISH 



greatest breadth towards the middle. Valves moderately convex, with or without a slight 

 median depression in the dorsal valve, which, when present, extends from about the middle 

 of the shell to the front. Ventral valve evenly convex, beak incurved and truncated by a 

 largish foramen, separated from the hinge-line by a deltidium in one piece ; beak-ridges 

 slightly rounded ; front margin straight or slightly biplicated. Surface smooth, marked 

 by concentric lines of growth. Loop short. A large specimen measured — 

 Length 1 inch 9 lines, width 1 inch, depth 8 lines. 

 Obs. This species bears some resemblance to Wold. Wanklyni ; but, besides being 

 referable to another genus, it may be distinguished by the shape of its beak and 

 deltidium, which in the shell under description is in one piece, while in W. Wanklyni it is 

 made up of two pieces. Although young and half-grown specimens show a complete 

 absence of biplication, a slight longitudinal depression is present in the dorsal valve of 

 some aged individuals. A fine series of specimens from the Lower Greensand of Upware 

 may be seen in the Woodwardian Museum, Cambridge. 



53. Terebratula Meyeri, Walker. Sup., PI. Ill, figs. 6 — 8. 



Terebratula Meyeri, Walker. Geol. Mag., vol. v, p. 401, pi. xix, fig. 6, 1868. 



Spec. Char. Shell longitudinally oval, greatest breadth and thickness about the 

 middle. Ventral valve convex, most so along the middle, where it forms a rounded 

 longitudinal fold or keel with lateral depressions. Beak very short, slightly incurved, 

 and usually worn from friction, caused by the shortness of its pedicle ; foramen large, and 

 separated from the hinge-line by a wide but narrow deltidium in one piece. Dorsal valve 

 convex, most so about the middle ; with a slight longitudinal depression commencing at 

 the umbo and widening as it nears the front ; lateral margin sinuous, and very much 

 curved backwards near the front. Surface smooth, marked by numerous, more or less 

 strongly indented, lines of growth. Loop simple, and very wide as compared to its 

 length. 



Length 18, width 13, depth 10 lines. 



Obs. This species is easily distinguishable by its shape from other Cretaceous forms 

 of the genus Terebratula, and especially so on account of the mesial fold in the ventral 

 instead of the dorsal valve. 



Position and Locality. T. Meyeri occurs in the Lower Greensand at Upware, in 

 Cambridgeshire. Mr. C. J. A. Meyer has found a specimen, which he believes may 

 be referable to the same species, in rocks of a similar age at Guildford. 



