- 158 - 



A. dariensis ; (l) it is larger, lees produced posteriorly-, tlie 

 curve of the anterior 'THrrrin is fuller, so "ftiat the ventral margin 



(1). Proc. Acad. Hat. Sci., Philadelphia, vol. 63, op. 352-365 

 pi. ^2, fig. 10, 1911. 



does not descend posteriorly; the type of sculpture is the same, 

 but neither the nodailerj or the -^onc^entric lines in the interspaces 

 are as prominent on right valves, on left valves the nelian rihs 

 are wider and the posterior rihs occasionallj? have tv/o rov73 of 

 fine nodules. 



Guppy's description, though brief, considered most of the 

 diagnostic features. His figure, however, was drawn from an im- 

 perfect valve; the incision of the uppermost oortion of the antero- 

 and postero- lateral margins is deeper than normal and the shell 

 should be more produced posteriorly. 



Occurrence.- lower Miocene: Bowden beds, Bowden, Jamaica. 

 (Guppy, 1866, 1874; Call, 1898) 



