86 



the left valve bends over the margin of the other, and 

 encloses about half of its base : the disk is rather rugged 

 when full grown. 



This occurs along with the last in what is called the 

 upper marine formation in Colvvell and Whitecliff Bays, 

 on the Isle of Wight. They have both been introduced 

 to notice by Professor Sedgwick. 



Figs. 5 and 6 are enlarged to three times the natural 

 length. 



CORBULA complanata. 



TAB. CCChXlL— Fio-s. 7 cmd 8. 



Spec. Char. Transversely oval, elongated, de- 

 pressed, and sulcated ; sulci few; anterior 

 side smallest, subtruncated, and defined by 

 an obtuse ridge ; left valve enclosing the 

 other. 



J. HE posterior part of the right valve is peculiarly flat- 

 tened and thickened : the surface is smooth between the 

 six or eight furrows that appear to be formed by periodical 

 interruptions of growth : the left valve is most convex ; 

 the lower edge of it encloses that of the other valve. 

 Length about half the width. 



Newly discovered by the Rev. G. R. Leathes in the 

 Crag at Roydon. It is rare. The outer coat is gene- 

 rally corroded, so as to give it a costated appearancej 

 a circumstance common in Crag fossils. 



