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opisthogyrate ; lumiile not differentiated, represented tiy a very 

 narrow, slightly flattened area; area iDehind the -umho wider, 

 flattened; rostral carina siti^ated near the dorsal ma.rgin, low, 

 relatively hroad, subrounded; distal third of the shell hearing 

 a very shallow sialcus iicnediateiy anterior to the rostral ray, 

 the sulcus very slightly emarginating the trmicated posterior 

 margin; external surface sculptured with fin, ir.pressed lines, 

 feebly developed on the umbones and accentuatec' by irregularly 

 spaced incrementals in the distal half of the shell; chondro- 

 phore large; teeth strong, becoming finer toward the p-?int of 

 divergence, the anterior series numbering about nineteen and 

 the posterior series fifteen; muscle scars and i^allial siniis 

 obscure. 



Dimensions .- Length, l"^. 5 mm.; alt., 7.5 mm.; semidiam. , 

 Remarks.- This species is conspicuous as being easily the 

 largest of the Bovden. Ledidae. Young shells display onl:; a 

 feeble posterior truncation below the blutit rostrum, but on mature 

 individuals this feature is especially prominent. Since the 

 pallial sinus is obsc:;re the proner position of this form is doubt- 

 ful; the shape, character of the external sciilpture and absence of 

 a well-defined lunule and sharp rostral carina suggest that it 

 may find its oroper place in the section Portlandiea of the genus 

 Yoldia - a section v/hich has been considered of generic v lue, 

 intermediate between Leda and Yoldia. 



