Nigerian Eocene Mollusca. 99 



there being no definite characters for a separation. Oppenheim's fig. la of 

 plate 1 8 of that species shows the interior of a lower valve containing- within it 

 an upper valve that has become inverted or placed out of position during the 

 process of fossilization, and which clearly indicates the presence of radial stria- 

 tions, suggesting the strong probability that it represents the opposing valve of 

 the same individual shell with which it is associated. The Nigerian valves 

 resemble very much in dimensions, those from Europe and Egypt, larger indivi- 

 duals exhibiting a height of 12, length 14, and diameter (with closed valves) of 10 

 millimetres. 



DISTRIBUTION. British : Middle Eocene (Lutetian) ; Europe : Eocene 

 (throughout) ; Egypt : Upper Mokattam Beds (Bartonian). 



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

 COLLECTOR. Mr. Kitson. 



Family CORALLIOPHAGID^. 1 



Coralliophaga eocenica, sp. nov. 



PLATE 11, figs. 4-5. 



DESCRIPTION. Shell extremely thin, narrow, elongately sub-cylindrical, 

 equivalve, dorsally arched, ventral margin incurved, postero-obtusely acuminate, 

 umbones very anterior, valves closed ; length more than three times the height ; 

 left valve with a laminate tooth parallel with dorsal margin and directed 

 posteriorly, right valve with a similar tooth but less prominent, succeeded 

 immediately in rear by two additional obscure teeth, also postero-obliquely 

 directed ; ligament linear, external ; pallial line angulately sinuated ; anterior 

 adductor scar prominent and rounded, posterior scar sub-central just beneath 

 dorsal margin, elongately elliptical ; surface concentrically ridged, finely inter- 

 lineated, posterior half of the valves polished internally. 



DIMENSIONS. 



Height .. ... ... ... ... ... ... 4 millimetres. 



Length ... ... ... ... ... ... ... 14 



Diameter (closed valves) ... 5 



1 M. Cossmann (Act. Soc. Linn. Bordeaux, 1911, Vol. 65, p. 83) has introduced the family name of 

 Lithophagellidae for Coralliopha$ra, which is considered to be irregular, because Gray's genus, Lithopha- 

 gella, being a synonym of the earlier Coralliophaga, of Blainville, should no longer be used either as a 

 family or generic name. 



7* 



