48 CRETACEOUS LAMELLIBRANCHTA. 



Affinities. — This species is easily distinguished from L. Tombechiana (see p. 45) 

 by its relatively higher and less inflated form, by the narrow ribs, and by the less 

 symmetrically placed ribbed area. 



In its narrow ribs L. Dwpiniana resembles L. subdequilatemlis, d'Orbigny (see 

 page 49) but the ribs in the latter are distributed over the greater part of the 

 shell and are more widely separated and more numerous. 



The specimens referred to L. semisulcata by Forbes are poorly preserved, but 

 probably belong to this species. 



Types. — From the Neocomian of Marolles (Aube) and Saint Sauveur (Yonne). 



Distribution. — Tealby Limestone (zone of Jl. brunsvicensis) of North Willing- 

 ham. Ferruginous Sands of Shanklin. Atherfield Beds of Redliill. Hythe Beds 

 of Hythe (fide Topley). 



Lima (Limatula) Fittoni, d'Orbigny, 1850. Plate VII, figs. 12 — 14, 15 a — c. 



1836. Lima semisulcata, J. cle C. Sowcrhy. Trans. Geol. Soc, ser. 2, vol. iv, 



pp. 336, 359 (not 129, 158), pi. 

 xi, fig. 10. 

 1850. — Fittoni, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 82. 

 1854. — semisulcata, J. Morris. Cat. Brit. Foss., ed. 2, p. 172 (partim). 

 1869. F. J. Pictet and O. Gampiehe. Foss. Terr. Cret. Ste. 



Croix (Mater. Pal. Suisse, 

 ser. 5), p. 166 (partim). 



Description. — Shell oval, moderately convex, higher than long, slightly in- 

 equilateral, with rounded margins, the posterior being more convex than the 

 anterior. Umbones small, close together. Ears equal. 



Ornamentation consists of from 13 to 15 radial ribs with sharp summits, 

 separated by narrow grooves. Pointed projections are present on the summits 

 of the ribs, especially near the ventral border of the shell. The anterior and 

 posterior parts of the shell are without ribs. The ribbed area is unsymmetri- 

 cally placed, and the anterior smooth part of the shell is considerably smaller 

 than the posterior part. Fine concentric ridges are seen on well-preserved 

 specimens. 



Measurements : 









(1) (2) (3) (4) (5) (6) 



(7) 



Length 



10 9 8 8 7 7 



6 mm, 



Height . 



16 14 14 13 12-5 12 



(1, 3 — 7) Upper Greensand, Haldou. 



(2) „ „ Blackdown. 



10 „ 



