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the yoimg of os:;-p:ontis of the same size; on left valves the 'diff- 

 erences are even sharper, since on elaehistus the rariials are 

 square and the interspaces almost sruarely impressed, v/hile on 

 ox y;? onus both ra^iials and interspaces are angiO-ar. left vslves 

 of the new s-oecies are less tumid than those of ox^^o-onus. 



OGCijirrence .- Lor/er i.lioeene: 3ov/den beds, 3ov.-den, Jamaica. 



