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 Colwell 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. CCCLX1I. — Figs. 7 and 8. 
Spec. Char. Transversely oval, elongated, de- 
pressed, and solcated ; sulci few; anterior 
side smallest, subtruncated, and defined by 
an obtuse ridge ; left valve enclosing the 
other. 
HIP 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 appearance, 
a circumstance common in Crag fossils. 
