Nigerian Eocene Mollusca. 93 



valves. There are, besides, no lateral teeth which, according- to Mayer-Eymar, 

 characterise the Egyptian shell. So far as sculpture is concerned both shells 

 exhibit a more or less zonal arrangement in the structure of the concentric 

 striations ; the closely-set radial striations are, however, absent in Egyptian 

 valves, althouo-h some distant obscure radial ribs are noticeable on the 



o 



posterior area of a valve as represented by Oppenheim's largest figure of 

 Tel Una zitteli. The Nigerian valves are thick and strong, being mostly 

 mineralised and consisting of a siliceo-calcareous structure. Relics of a 

 periostracum are frequently preserved. This form is regarded as belonging 

 to Poli's genus Peronaea on account of its non-rostrate character, its more or 

 less trigonal shape, and its possession of a nearly horizontal pallial sinus, this 

 latter character being much rounder and more expansive in Arcopagia, with 

 which Oppenheim associated M ay er-Ey mar's Egyptian shell of Tellina zitteli. 



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



COLLECTOR. Mr. Kitson. 



Family MACTRID^. 

 Mactra semisulcata, Lamarck. 



PLATE 7, figs. 10-13. 

 Mactra semisulcata. 



Lamarck : Ann. Mus. Hist. Nat. (Paris), 1805, Vol. 6, p. 412, and 1807, Vol. 9, pi. 18 (20), fig. 3 ; 

 Deshayes : Desc. Coq. Foss., Paris, 1824, Vol i, pi. 4, figs. 7-10, p. 31, ibid., Suppl. 1857, Vol. i, p. 288; 

 Dixon's "Sussex," 1850, pi. 3, fig. 10, p. 88; Cossmann : Ann. Soc. R. Mai. Belgique, 1886, Vol. 21, 

 p. 60 : and R. B. Newton : Syst. List, &c., 1891, p. 84. 



REMARKS. Several moderately sized and smaller shells, forming part of 

 this collection, are easily referred to this European species. The valves are 

 deeper than in M. compressa of Deshayes ( = M. depressa, Deshayes non 

 Lamarck), besides exhibiting the equally strong striated character of the 

 lunule and escutcheon regions which is so marked a feature of the species. 

 Variations in size show a length and height respectively of from, 19 x 13 to 

 30 x 21 millimetres, whilst one of the largest European examples in the 

 British Museum measures 50 x 40 millimetres. 



DISTRIBUTION. Eocene : according to M. Cossmann this species is found 

 throughout the Eocenes of France ; it is also recorded from the Lutetian 

 beds of England (Bracklesham Bay). 



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

 COLLECTOR, Mr. Kitson. 



