72 R. BULLEN NEWTON on 



Family GLYCYMERID/E. 



Glyoymeris nigeriensis, sp. nov 



PLATE 8, figs. 8-10. 



DESCRIPTION. Shell elongately quadrangular, length one-fifth more than the 

 height, inaequilateral, compresso-convex, margins clentated, both sides obliquely- 

 truncated, posterior shortest with postero-ventral angulation ; ligament region 

 about half the length of shell, narrow, without divergent grooves, vertically 

 and equally costated ; hinge line horizontal, not arched, half the length of 

 shell, with a terminal curvature bearing about twenty-five denticles on each 

 side, which are small and nearly obsolete in the centre ; adductor scars 

 unequal, anterior largest and most oval ; outer surface with numerous equal, 

 radial costae minutely annulated by the close concentric striations covering 

 the valves. 



DIMENSIONS. 



Young. Adult. 



Height ... ... ... 10 ... 1 6 millimetres. 



Length 13 ... 20 



Diameter (closed valves) 6 ... 12 



REMARKS. In general contour and appearance this form resembles 

 Pectunculus decussatns of J. Sowerby, 1 from the Lower Eocene (London Clay) 

 of Highgate. There are, however, some important differences. The Nigerian 

 shell is more elongate ; its ligament region is linear, not triangular ; the hinge 

 line is horizontal, not arched ; the radial costae are less numerous, without 

 intermediate riblets, delicately annulated by the close concentric striations 

 which cover the valve, but not nodulated ; margins dentated, not smooth. 

 Such distinctions are deemed of sufficient importance to separate this shell 

 from the British form. 



OCCURRENCE. Cuttings Nos. 5, 6, 10, 11, 12, 13, 15. 

 COLLECTOR. Mr. Kitson. 



1 Mineral Conchology, 1813, Vol. i, pi. 27, fig. i, p. 71. 



