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SUPPLEMENT TO THE BRITISH 



45. Terebratula depressa, Lamarck. Dav., Cret. Mon., PI. IX, figs. 9 — 24; Sup., 



PI. IV, figs. 1 and 3, 4. 



Terebratula depressa, E. R. Lankester. The Geologist, vol. vi, p. 414, pi. xxi, 



figs. 4—6, 1863. 



— — C.J. A. Meyer. Geol. Mag., vol. i, pi. xi, fig. 1 5, 1864. 



— — J.F. Walker. Ib., vol. v, p. 403, pi. xviii, figs. 2, 2 a, 1868. 



— — J. W. Judd. Quarterly Journal Geol. Soc, vol. xxiii, 



p. 245, 1868. 



At page 29 of my Monograph I described the typical form of T. depressa (Lamarck) 

 as found in the " Sponge-gravel " of Faringdon, and agreeing in every respect with 

 specimens that occur in the Tourtia of Tournay, Montignies-sur-Roc, and Gussignies, in 

 Belgium. Since that period much larger and better examples of the typical form have 

 been found in the Lower Greensand at Upware. The shell varies greatly in shape, the 

 beak being in some specimens very much elongated and tapering, whilst in other examples 

 it is short and rounded. A great difference is also observable in the degree of convexity 

 of the dorsal valve. In some specimens there exists a mesial fold without any depression 

 along its middle, while in other examples a shallow longitudinal depression is observable 

 along the middle of the fold, giving the valve a slightly biplicated appearance. 



Mr. Walker has therefore proposed to apply varietal designations to two or three of 

 these modifications of T. depressa, which he regards as sub-species. 



Typical forms of T. depressa have been described by Mr. E. R. Lankester and C. J. 

 Meyer from the Lower Greensand (Folkstone beds or Upper Neoconiian) of Shanklin, 

 Isle of Wight, and of Guildford, Surrey. Mr. J. W. Judd and Mr. Walker have found 

 the same shell in the Middle Neoconiian at Tealby, in Lincolnshire. I was therefore 

 mistaken when, at p. 71 of my Monograph, I placed this species in the Upper Greensand. 

 Messrs. Pictet and De Loriol have met with well-characterised and large specimens in the 

 "Etage Aptien" at St. Croix, Switzerland. I have also a specimen from the Lower 

 Greensand of Essen-an-der-Ruhr. 



I will now reproduce Mr. Walker's descriptions of his several varieties of T. depressa. 



46. Var. uniplicata, Walker. Sup., PI. IV, figs. 2, 5, 5 a. 



Walker, Geol. Mag., vol. vii, 1870, p. 561, figs. 1, 2. 



"Shell somewhat triangular in form, with one wide mesial fold; surface smooth, 

 marked by faint concentric lines of growth ; greatest width about the middle of the 



