154 CRETACEOUS LAMELLIBRANOHIA. 



anteriorly. Ridges extend from the umbo to the angles at the margin of the 

 valve ; the parts between the ridges are flattened. Lunule large, ovate, divided 

 into an inner and an outer part by a ridge. Escutcheon very large, consisting of 

 a median lanceolate part which is much depressed and separated by a sharp edge 

 from a large concave outer portion. 



Ornamentation consists of broad concentric ridges which run parallel to the 

 margin of the valve and end abruptly at the lunule and escutcheon. Very fine, 

 sometimes indistinct, ribs occur on the ridges and interspaces. 



Affinities. — Lucina sculpta is quite unlike any other Cretaceous species. Its 

 angular outline and large concave escutcheon give it an unusual appearance. 

 Externally it shows some resemblance to some species of Tliyasira? but the hinge 

 and adductor impressions are at present unknown. Stoliczka regarded it as 

 probably a true Lucina. 



Remarks. — I have seen only four specimens, of which three are in the British 

 Museum and one is in the Museum of Practical Geology. 



Type. — The type cannot be found. It is stated to have come from the Speeton 

 Clay (? zone of Belemnites minimus). 



Distribution. — Lower Gault (Bed vi) of Folkestone. 



Lucina tbneba {Sowerby), 1836. Plate XXIV, figs. 10—14. 



1836. Venus ? tenera, J. cle C. Sowerby. Trans. Greol. Soc., ser. 2, vol. iv, pp. 114, 



335, pi. xi, fig. 7. 

 1854. J. Morris. Cat. Brit. Foss., ed. 2, p. 231. 



1865. (? Lucina), F. J. Pictet and G. Campiche. Foss. Terr. 



Crt't. Ste. Croix (Mah'r. 



Pal. Suisse, ser. 4), p.189. 



1870. (PCaeyatis), F. StoUczha. Palaeont, Iiuliea, Cret. Fauna 



S. India, vol. iii, p. 160. 

 1875. Lucina A. J. Jukes-Browne. Quart. Journ. Geol. Soc, vol. xxxi, p. 



300, pi. xv, figs. 10—12. 



Description. — Shell oval, moderately convex, longer than high, inequilateral, 

 the anterior part longer and higher than the posterior part. Anterior margin 

 regularly rounded, passing gradually into the curved ventral margin. Posterior 

 margin somewhat truncated, forming an obtuse angle with the postero-dorsnl 

 margin. Umbones of moderate size with a slight forward curvature. Lunule 

 elongate, depressed, limited by a carina. Escutcheon large, not distinctly limited. 



1 Axinus, Sowerby; Crypto(lon,Tnv\<n\. 



