tionately higher, more convex with higher and more incr^ryed iim- 

 bones, more ercavate'l posterior dorsal marg'in, longer posterior 

 trivficatiou, ricler posterior slope, more nxinierous and finer um- 

 honal concentric undulations, \-hile the tmdulstions on the anter- 

 ior slope are coarser, there "being no ahrupt change from one ser- 

 ies to the other, such ts is very prominent on densus. 'the pres- 

 ent form is readily distinguished from the associated lamaicensis 

 by its rreater thielcness, more elongate OTitline, greater convexity, 

 more escavated posterior dorsal margin, more incurve' umbo, the 

 presence of concentric undulations on only the upner half or less 

 of the anterior slope and the greater prominence of the right 

 posterior cardinal. 



Occu.rrence »~ lower Kiocene : "Rowden beds, "Bovi'den, Jamaica. 



