112 



PLAGIOSTOMA Iseviiisculum. 



TAB. CCCLXXXII. 



Spec. Char. Transversely obovate, oblique, 

 convex, longitudinally ribbed ; ribs close, 

 broad, irregular, very little elevated, con- 

 vex; anterior slope straight, hollow; ears 

 small, unequal. 



A. smooth even formed shell, distinguished by the 

 slight elevation of its ribs, if the radiating risings can be 

 allowed the name of ribs, and the total absence of any 

 striae between them ; the lines of growth are numerous^ 

 but very slightly marked ; the shell is thin so that the 

 edge is undulated. 



Not uncommon in the Pisolite of Malton ; it is one of 

 the many very distinct species so improperly confounded 

 with P. rigidum by the Authors of a Geological Survey 

 of the Yorkshire Coast, who have besides indulged them- 

 selves in changing names, and several other liberties too 

 palpably induced by error to merit particular notice. 



