Nigerian Eocene Mollusca. 61 



examples. These younger forms are numerously represented, the one of least 

 dimensions being an upper valve with a length and height respectively of five 

 and seven millimetres ; it exhibits a finely crenulated margin. In the original 

 account of this species, S. V. Wood overlooked an important element of 

 sculpture in the upper valve, in connection with the presence of closely 

 arranged radial costae, such as ornament the other valve, although considerably 

 depressed and rendered much less obvious on account of the great prominence 

 of the concentric laminae ; this structure is well seen on Wood's figured 

 specimen (Fig. 2a, of PL 5) which gives, however, only an internal view of 

 the upper valve. It is difficult to accept Wood's species as synonomous with 

 O. extensa of Deshayes ' from the Upper Eocene (Bartonian) of France as 

 recommended by M. Cossmann, 2 who assumes that the original figures of the 

 interior of that species probably represented O. gigantica on account of the 

 absence of crenulated margins. The smooth character of the margins of 

 O. extensa was, however, well emphasised in the first description, as marginibus 

 integris, and again referred to in the later work of Deshayes, 3 who regarded 

 the species as distinct from O. elegans which possessed crenulations. The 

 presence of radial ribs on the upper valve, now pointed out for the first time, 

 will further support the contention that O. marginidentata is a perfectly good 

 species and not to be amalgamated with (9. extensa. The present specimens 

 chiefly differ from the type in their narrower and more oblong contour. 



DISTRIBUTION. Eocene (Lutetian-Bracklesham Beds) England. 

 OCCURRENCE. Cuttings Nos. i, 5, 6, 10, 15. 

 COLLECTORS. Sir F. Lugard ; Mr. Kitson. 



Ostrea cf. ludensis (Deshayes). 



PLATE 8, figs. 2, 3. 

 Ostrea ludensis. 



Deshayes : Desc. Anim. Sans Vert. Coq. Foss. Paris, 1861-64, Vol. 2, pi. 85, figs. 1-4, p. 107. 



REMARKS. In the collection is an isolated upper valve of an Ostrea 

 which appears to share the characters of this species. It possesses a smooth, 

 minute, subacute, rounded prodissoconch, furnished with distant concentric 



1 Description des Coquilles Fossiles des Environs de Paris, 1832, Vol. I, p. 358, pi. 56, figs. I, 2. 

 3 Catalogue Illustre des Coquilles Fossiles de 1'Eocene des Environs de Paris : Ann- Soc. R. Mai. 

 Belgique, 1887, Vol. 22, p. 194. 



3 Description des Animaux sans Vertebres, &c., 1861, Vol. 2, p. 117. 



