.:. OO 



!RemarkG_.- !rhe or.tline and width s-re quite variable; tlie 

 dorsal mar ""in roay "be subangiilar , as in the c tse of the t^-pe 

 ( with the angulation Gituated at ahout a third of the 'Hs- 

 tance from the u ho to the pes terior inar^-in) or ahtuptly con- 

 ve-c, in whioh oaae the shell is wider. In a similar manner the 

 ventral margin varies from decide''' concave throughout to concavo- 

 convex, the latter outline "being caused ■"■ '-he reflection of the 

 posterior portion. The socket on the hirjge of the left valve 

 ir? pronouncerl, hut none of the rirht valves. have a "-ell-develoo- 

 ed corresr)ondiiTg toot: . Jor 3o-ventrall;>- the shell "- ost eon- 

 vex near the ventral mar^:"in, while in an ant ero- posterior line 

 the greatest convexitj^ i s at about the middle of the shell. 



The Pleistocene (1) and Recent D. cochleata Eickx (2), 

 from the east coast of the Panama region, is so close that 



(1). Brown, A. P. and Pilshr^-, '-I, A., Proc. Acad. Lat. Sci. 

 Philadelphia,, vol. 63, p. 497, 1913. 



(E). 



the tv;o forms can hardly he separated; the Bov/den form, is, hovr- 

 ever, smaller, more slender and in general more abruptly convex. 



Occurrence .- lower Kiocene ; Bov/den beds, Bowden, Jamaica. 



