GREY CHALK MARL. 129 



mination of concentric laminjE. The shell is very thin, and possesses a 

 glossy appearance; the width and length are nearly equal. 



Tab. xxvi. fig. 8, a fine specimen, with the shell entire. 



fig. 22, is probably the under valve of this species. 



Locahties. Hamsey, Stoneham. 



55. Pecten Tab. xxvi. fig. 7. 



Although the valve here figured is perfect, yet as it only exhibits the 

 inner surface, and resembles in form several other shells of the genus, the 

 species cannot at present be ascertained. 



Locality. Hamsey. 



56. Plagiostoma? aspera. Tab. xxvi. fig. 18. 



Subdepressed, obovate, with numerous longitudinal, aculeated sulci. 



To the naked eye, this shell appears as if marked with smooth, longi- 

 tudinal striae, but conveys a sensation of roughness to the touch. With 

 the assistance of a lens, the striae are perceived to be sulci, dividing the 

 surface into flat ribs, the edges of which are fringed with minute sharp 

 points. It has a few irregular lines of growth : the structure of the hinge 

 is not shewn in any of the specimens in my possession. 



This shell bears considerable resemblance to Lima spathula of Lamarck. 



Localities, Hamsey, Stoneham : rare. 



57. Plagiostoma . Tab. xix. fig. 1. 



The cast of a transversely ovate, depressed bivalve, apparently of this 

 genus. It has fifteen prominent costae, which diverge from the beaks to 

 the margin ; the latter is undulated. 



Locahties. Hamsey, Middleham. 



58. Plicatula *j9mo*a. Tab. xxvi. figs. 13. 16, 17. 



" Ovate, depressed, spinous ; spines adpressed, smallest on the deeper 

 valve, margin entire*." 



The specific description is that given by Mr. Sowerby ; the Sussex 

 specimens being imperfect, and differing in some partixiulars from those 

 figured in the Min. Conchology. The latter are described as being 



* Min. Conch. Vol. iii. p. 79. 



