46 CRETACEOUS LAMELLIBRANCHIA. 



? 1854. LIMA SEMISULCATA, J. Morris. Cat. Brit. Foss., ed. 2, p. 172 (jjartini). 

 1855. TOMBECKIANA, G. Cotteau. Moll. Foss. de 1'Yonne, p. 100. 



1861. P. de Loriol. Anim. Invert. Foss. Mt. Saleve, p. 95, 



pK xi, fig. 11. 



1869. P. de Loriol and V. Gillieron. Urgon. infer, de 



Landeron, p. 19, pi. i, fig. 17. 

 F. J. Pictet and G. Campiche. Foss. Terr. Oct. Ste. 



Croix (Mater. Pal. Suisse, ser. 5), p. 148. 



1871. RADULA (LIMATULA) TOMBECKIANA, F. Stoliczka. Palseont. Indica, Cret. 



Fauna S. India, vol. iii, p. 414. 

 LIMA TOMBECKIANA, W. A. Ooster. Protozoe Helvetica, vol. ii, pp. 104, 



123, 140. 



1883. W. Keeping. Foss., etc., Neoc. Upware and Brick- 



hill, p. 111. 



Description. Shell oval, inflated, higher than long, produced a little more 

 anteriorly than posteriorly. Umbones rather small, close together. Ears equal. 

 Margins of valves rounded, the posterior with a greater curvature than the 

 anterior. 



Ornamentation consists of from 13 to 16 strong, rounded or slightly keeled 

 ribs separated by narrow grooves. The ribs are confined to the median part of 

 the shell, and the anterior and posterior parts are without ribs. The ribbed portion 

 is not quite symmetrically placed, the anterior smooth portion being rather larger 

 than the posterior smooth portion. Very fine concentric ridges are present on the 

 shell, and may form scale-like projections where they cross the ribs. 



Measurements : 



(1) (2) (4) (5) (G) 



Length 9 9 8 8 7 11 mm. 



Height 12 11 12-5 13 10 15-5 



(1 5) Hythe Beds, Court-at-Street. 

 (6) Lower Greensand, Brickhill. 



Affinities. Some specimens of L. Tombecldana approach very closely L. 

 Fittoni from Blackdown and Haldon (see p. 48), and it is quite possible that the 

 latter is only a local variety of the former since some examples found in the Upper 

 Greensand of Charm outh and Potterne (Plate VII, fig. 10) seem indistinguishable 

 from L. Tombecldana. As a rule L. Tombecldana differs from L. Fittoni in having 

 the ribbed part of the shell more nearly symmetrical in position, in the shell being 

 rather longer and rather more convex with the umbonal part more pointed, and 

 in the ribs being more rounded. 



L. Tombeckiana differs from L. semisulcata, Nilsson, in being smaller, relatively 

 longer, less symmetrical, and with the umbonal part more pointed. In this con- 

 nection, however, it should be noted that Hennig 1 considers that specimens which 

 1 Eevis. Lamellibr. i Nilsson's ' Petrific. Suecana ' (1897), p. 29. 



