Nigerian Eocene Mollusca. 69 



a minute triangular fossette under the beaks, besides possessing a larger 

 trellised ornamentation on the left valve than on the right. These Eocene 

 forms, however, differ from the present shell in their more oblong contours, 

 much smaller dimensions, and being furnished with the central fossette. 

 There is another Eocene shell that has been distinguished by M. Cossmann 

 as Scapularca? the type of which is Area scapulina, Lamarck, which presents 

 similar ligamental features to the Nigerian shell, but it differs in being much 

 more inaequilateral, in its modioliform shape, and smaller size. With such 

 distinctions to consider, it is difficult to accurately place the Nigerian shell, 

 although as its general conformation and ligament features resemble Fossularca 

 and, in part, the two sections of Galactella and Scapularca, it is proposed that 

 it be recognised under the first-named genus which was established many 

 years before the others. It should be also mentioned that the ligament 

 region of this shell is similar in structure to that of Anadara nigeriensis 

 described in this paper. The shell is of abundant occurrence in the Nigerian 

 deposits, while its valves are frequently perforated, as in Striarca africana, 

 and chiefly in the umbonal region where certain organisms have probably 

 attacked it for the extraction of the soft parts of the mollusc. 



OCCURRENCE. Cuttings Nos. i, 2, 5, 6, 10, n, 12, 13, 14, 15. 

 COLLECTOR. Mr. Kitson. 



Striarca africana, sp. nov. 

 PLATE 8, figs. 11-13. 



DESCRIPTION. Shell thin, subcylindrical, without mesial depression, slightly 

 inequivalve, subequilateral, length twice the height ; dorsal and ventral 

 margins parallel, anterior rounded, posterior truncated, widely and obtusely 

 carinated ; ligament region entirely covered by the lozenge being narrowly 

 lanceolate, horizontally lineate and perpendicularly striated ; surface sculpture 

 similar in both valves, microscopically reticulate, consisting of closely set, 

 strong, concentric costae, crossed by innumerable minutely granulated radial 

 striations of which the more prominent are equi-distant, inner margins smooth ; 

 umbones prosogyrous, acute, incurved, moderately distant ; hinge line horizontal, 



1 Act. Soc. Linn. Bordeaux, 1912, Vol. 66, p. 312. 



