9O R. BULLEN NEWTON on 



sloping posterior side, and in being furnished with a crowded series of thread- 

 like striations instead of the flattened lines of growth as in Lamarck's shell. 

 It agrees with the French species in exhibiting obscure microscopical radial 

 striations, a structure seen also in recent forms of this genus, and particularly 

 mentioned in modern years by the late Jukes-Browne l in connection with 

 his studies on the " Veneridae." Another point of difference between these 

 two species may be observed in the structure of the pallial sinus which is 

 rounded or obtusely acuminate in the form from Nigeria, while in the 

 European shell it has frequently a squarish termination with angulate corners. 

 The dental elements are the same in both species and agree with those 

 present in the genus Callista, under which M. Cossmann 2 includes C. 

 laevigata. This is an abundant shell in the Nigerian deposits and is generally 

 well preserved. 



OCCURRENCE. Cuttings Nos. 2, 6, 10, 12, 13. 

 COLLECTOR. Mr. Kitson. 



Tivelina of. sphenarium (Bayan). 



PLATE 9, figs. 7-10. 

 Cytherea cuneata. 



Deshayes : Desc. Coq. Foss., Paris, 1825, Vol. I, pi. 22, figs. 6, 7, p. 131 ; ibid., Suppl., 1858, 

 Vol. I, p. 465, non Lamarck. 



Cytherea sphenarium. 



Bayan : fetudes Coll. Ecole. Mines Foss., 1873, Fasc. 2, p. 121. 



Tivelina sphenarium. 



Cossmann: Ann. Soc. R. Mai. Belgique, 1886, Vol. 21, p. 122. 



Meretrix (Tivelina) sphenarium. 



Cossmann & Pissarro : Iconog. Coq. Foss. Eocene, Paris, 1904, Vol. i, pi. n, fig. 35. 



REMARKS. This is another of the very abundant Pelecypods which occur 

 in the Nigerian deposits, the valves exhibiting every possible size and varying 

 in length and height respectively of from 7 x 5 up to 20 x 17 mm., their 

 diameters with both valves in the closed condition ranging from 4 to 

 12 mm. The valves are slightly higher than those of European examples 

 although preserving the characteristic subtrigonal contour, the posterior side 

 being the most produced, as it is also truncated, and obtusely angled, whilst 



1 Proc. Mai. Soc., London, 1908, Vol. 8, p. 154. 



2 Ann. Soc. R. Mai. Belgique, 1886, Vol. 21, p. 113 (101). 



