Nigerian Eocene Mollusca. 89 



contour being less ovate, in the possession of a steeper obliquity to the 

 posterior side, and in its less regular concentric sculpture. 



It should be mentioned that the late A. J. Jukes- Browne regarded the 

 European species referred to, together with C. suberycinoides of Deshayes, as 

 belonging to Meek's section, Macrocallista 1 (Type Venus gigantea, Gmelin), 

 being alike in general shape and hinge characters. For the same reason, 

 therefore, the present new species would be also included in the same section. 



OCCURRENCE. Cuttings Nos. 10, 5, 6. 

 COLLECTOR. Mr. Kitson. 



Callista kitsoni, sp. nov. 

 PLATE 9, figs. 11-14. 



DESCRIPTION. Shell thin, ovato-transverse, inaequilateral, posteriorly elon- 

 gate and oblique, moderately inflated ; lunule lanceolate, distinct, not impressed ; 

 surface bearing numerous fine, close, concentric, often irregular, striations, 

 together with obscure microscopical radial striae ; umbonal regions tumid ; 

 hinge plate narrow ; left valve with a strong, compresso-triangular tooth in 

 front, a pair of cardinals diverging from the dorsal arch, and a short oblique 

 laminar tooth in rear ; right valve with an elongate anterior socket for the 

 front tooth of opposing valve, a pair of closely parallel cardinals with flattened 

 opposing faces, followed by a thick posterior cardinal obliquely sulcated above ; 

 pallial sinus wide, ovate, obtusely acuminate, and nearly horizontal. 



DIMENSIONS. 



Young. Adult. 



Height... ... ... ... 12 ... 20 millimetres. 



Length ... 17 27 



Diameter (united valves) ... 9 ... 14 



REMARKS. This species is closely related in its internal characters to 

 Cytherea laevigata, Lamarck 2 from the Anglo- Parisian Middle and Upper 

 Eocene deposits. It differs, however, in having thinner valves, being less 

 elongate and rather more convex, in possessing a shorter and more abruptly 



1 F. B. Meek : Invertebrate Cretaceous and Tertiary Fossils, Upper Missouri Country Kept. 

 United States Geol. Surv. Territories, 1876, Vol. 9, p. 179. 



2 Ann. Mus. Hist. Nat. (Paris), 1806, Vol. 7, p. 134 ; ibid. 1808, Vol. 12, pi. 21 (40), fig. 5. 



