202 UPPER, OR FLINTY CHALK. 



The length of this shell exceeds its width ; it is slightly oblique, and 

 the surface is covered by numerous diverging ribs, and furrows, decussated 

 by fine transverse stri^ : the hues of growth are deep, and frequent. 



The lower valve is convex, beaked, and of a pentangular form ; a large 

 costa is placed on each angle, and four lesser ones on each of the inter- 

 vening spaces. The beak is produced, and incurved. The upper valve 

 is flat, rather depressed, and marked with diverging costae, and sulci, 

 corresponding in number with those of the lower valve. The hinge hue 

 is straight. The sides diverge from the beak towards the front, the 

 margin of which is pentangular, and arcuate. 



Tab. xxvi. fig. 20. A perfect specimen of both valves. 



fig. 19. Inner surface of the upper valve. 



fiff. 14. A view of the back of the lower valve. 



Locahties. Upper, and Lower chalk, near Lewes, and Brighton ; it also 

 occurs in the ferruginous sand of Kackham common. 

 65. Pecten nitida. Tab. xxvi. figs. 4. 9. (1 ?) 



Obovate, rather oblique, longitudinally striated ; striae numerous, 

 radiating ; upper valve flat ; lower valve shghtly convex. 



A remarkably neat shell, much depressed, and rather obhque. The 

 upper valve is perfectly flat ; the lower one slightly convex. The striae 

 are prominent, and regular, radiating from the hinge line to the margin ; 

 about fifty on each valve. These are crossed by fine hues, which are 

 scarcely visible to the naked eye. The margin is slightly crenulated, the 

 ears are small, and placed obliquely ; the lines of increase few, and in- 

 distinct ; the length and width of the shell nearly equal. 



Tab. xxvi. fig. 4, the inner surface of the lower valve ; and fig. 9, the 

 external surface of the flat valve ; part of the lower shell is also seen, the 

 upper valve being somewhat displaced. 



fig. 1, represents the inner surface of a pecten, bearing 



considerable resemblance to the present species. Where portions of the 

 shell have been removed, the impressions of the outer surface remaining 

 upon the chalk, indicate the existence of strise like those of P. nitida. The 



