Nigerian Eocene Mollusca. 81 



being- equal to that of the divisional furrows, except immediately below the lunu- 

 loid area, where they become almost contiguous. Numerous close and rather 

 coarse concentric striations cover the whole surface, the costae being thus 

 furnished with annulations, especially on the anterior and ventral regions, where 

 they are strongest. This ringed appearance of the costae is not so apparent in 

 the true C. planicosta because the concentric striae are somewhat finer, moreover 

 the radial ribs of that species are more numerous than in the present shell. 



DIMENSIONS. 



Height ... ... ... ... ... ... ... 13 millimetres. 



Length ... ... 15 



Diameter (of single valve) ... ... ... ... 5 



The valve is moderately convex and of rhomboidal contour, while the hinge, 

 which is small and narrow, contains a prominent triangular cardinal tooth with a 

 socket on each side for the reception of the teeth in the opposing valve ; the 

 crenulations of the inner margins are well displayed. It appears to be a young 

 example, but until further evidence is available its true determination must remain 

 in abeyance. L)r. Carlotta Maury has identified C. planicosta in the Antillian 

 Eocene of Trinidad. 



DISTRIBUTION. Eocene of Britain, Europe, N. America and Trinidad. 

 OCCURRENCE. Cutting No. 10. 

 COLLECTOR. Mr. Kitson. 



Cardita costaeirregularis, sp. nov. 

 PLATE 9, figs. 30, 31. 



DESCRIPTION. Shell strong, sub-triangular, closed, inequilateral, depresso- 

 convex, length about i/5th in excess of altitude ; anterior region short, oblique, 

 depressed with small lunule, posterior end produced, depressed, bearing a short 

 and narrow ligament furrow ; cardinal area small, dentition as in C. costae- 

 nodulosis ; sculpture exhibiting from 10-12 contiguous radial costae at each end, 

 much depressed posteriorly, but anteriorly broad and well rounded, sides of the 

 valves with two isolated, radial and rounded ribs divided by unequally wide 

 furrows, surface of valves strongly and concentrically striated throughout, ventral 

 margin widely plicated, anterior and posterior margins closely pectinated ; internal 

 surface radially swollen and furrowed. 



6 



