Nigerian Eocene Mollusca. 91 



the anterior margin is vertical, oblique and ventrally rounded. An obscure 

 and almost obsolete shallow depression runs obliquely from the umbonal 

 region to the postero-ventral corner causing- a slight insinuation at the 

 margin, a character usually found in species of Tivelina although apparently 

 not present in T. sphenarium, but which is quite obvious in Cytherea rustica, 

 Deshayes and C. tellinaria, Lamarck, both referred by Cossmann to 

 Tivelina from the French Eocenes, species which, nevertheless, differ from the 

 present Nigerian shell in the possession of more elongately oval contours. 

 The original figures of C. cuneata, Deshayes, a name altered by Bayan to 

 C. sphenarium on account of Lamarck's pre-occupation of the former for 

 another shell, are by no means good, a better conception of the outline being 

 available in MM. Cossmann and Pissarro's work referred to above. The 

 type specimen was most probably very eroded as the concentric striations 

 appear to be confined to the posterior margin instead of being continued 

 across the valve whilst an exaggerated curvature is given to the ventral 

 region which is not maintained in actual specimens. Tivelina was founded 

 by M. Cossmann, in 1886, on Lamarck's Cytherea tellinaria, a number of 

 other species being also included in it ; it is regarded as being restricted to 

 Eocene times and occurs throughout beds of that age in Europe, undescribed 

 species occurring also in the Barton Beds of England. The present 

 specimens are much better preserved than most European examples of 

 Tivelina available for study in the British Museum, so that the more or less 

 regular concentric sculpture, the large lanceolate lunule, the short pallial sinus, 

 and the dental elements, are all remarkably clear and well defined. 



DISTRIBUTION. Upper Eocene : Europe. 

 OCCURRENCE. Cuttings Nos. i, 2, 5, 6, 10, 15. 

 COLLECTOR. Mr. Kitson. 



Family TELLINID^. 



Peronaea nigeriensis, sp. nov. 



PLATE n, figs. 1-3. 



DESCRIPTION. Shell trigoniform, broad and ovately oblong, nearly equi- 

 lateral, more or less smooth, plano-convex, obtusely angulate posteriorly, 

 anterior border the most produced and pursuing an obliquely linear direction 



