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LEDA (HE^EIEDA) DUEKDMI n. sp. 



Desoription .- ^hell small, polishet^, to imderl -til angular 

 with a short posterior rostrum, decidedly convex, suh equilateral ; 

 posterior dorsal margin slightly concave; bluntly rounded anter- 

 iorly; ventral margin asymmetrically arcuate, being slirrhtly more 

 convex posteriorly; umbones ^igh, tumid, strongly opisthogyrate ; 

 area behind the umbo distinctly flattened; rostral carina lov/, 

 broad, but strong *^J^oughout ; e:-ternal sirrface s c lil ot ure d with 

 fine, evenly spaced, concentric lines except on top of the umbones 

 and in the area bounded by the rostrsl carina- the sculpture at 

 times obsolete on the posterior half or entire surface of the 

 shell; chondrophore large, triangular, situated below and Just 

 anterior to the tip of the umbo; teeth strong, the anterior 

 series numbering- about thirteen and the posterior sixteen. 



Dimensions .- Length 4.9 mm.; alt., 5.4 mm.; semidiam. , 

 ,9 mm. 



Remarks .- I. duerdeni has a facies totally different from 

 bowdeniana ; it is smaller, higher, and has a shorter, but more 

 acute, rostrum, stroi^ger ventral carina, more regular and more 

 delicate external sculpture, larger chondrophore and heavier hinge. 

 In outline it stands in decided contrast with the average leda and 

 without the testimony of the ligament wo ;ld probably be placed 



