Nigerian Eocene Mollusca. 71 



sculpture exhibiting thirty distant radial costae and equal furrows, costal 

 summits more or less depressed, especially ventro-laterally, covered with close 

 concentric striations which are thick in the earlier growth of the shell but 

 which afterwards become thinner, closer and distinctly scalloped, the postero- 

 umbonal grooves frequently furnished with delicate radial striae composed of 

 minute elongate tubercles ; hinge line straight or slightly arched bearing about 

 forty-five denticles nearly equally divided on each side ; denticles small and 

 verticle in the centre, laterally divergent, sometimes bent at the middle, very 

 coarse in aged specimens and often grooved or bifurcated above, especially 

 posteriorly ; adductor scars well defined, posterior the largest, subquadrate ; 

 margins closed and dentated. 



DIMENSIONS. 



Young. Adult. 



Length 12^ ... 42 millimetres. 



Height 10 35 



Diameter (closed valves) ... 8i ... 32 ,, 



REMARKS. This shell is associated with Gray's 1 genus Anadara, the type 

 of which is Area antiquata of Linnaeus of existing seas, on account of its 

 squarish contour, the possession of equi-sized valves, and the general details 

 of sculpture. Similarly, it also resembles Scapharca of Gray * founded on 

 Bruguiere's Area inaequivalms, a recent species although clearly distinguish- 

 able, from the fact that the valves of the latter are of unequal dimensions. 

 The features of the ligament furrow, however, connect the Nigerian shell 

 more closely with Cossmann's Fossularca 2 and its sections Galactella and 

 Scapularca, rather than with Anadara, because of its perpendicularly striated 

 surface and the total absence of chevrons, the latter being nearly always 

 present on both Anadara and Scapharca. In general appearance this type of 

 shell belongs to Miocene and Recent seas rather than to an older period of 

 time, although small forms of Anadara have been recognised by Cossmann in 

 Eocene rocks. The valves vary much in size and are abundantly represented 

 in the collection. 



OCCURRENCE. Cutting Nos. i, 2, 5, 6, 10, n, 12, 13, 15. 

 COLLECTOR. Mr. Kitson. 



1 Proc. Zool. Soc. 1847, p. 198 



2 Ann. Soc. R. Mai. Belgique, 1887, Vol. 22, p. 138, and Act. Soc. Linn, Bordeaux, 1912, Vol. 66, 

 p. 312. 



