- 274 - 



end; postero-dorsal margin longer, straight or slightly convex, 

 with a steeper slope; posterior end more attenuated than the ant- 

 erior, rotuidp'^ ■'■0 p-'T^-^-'^imoated ; hp^'^' -\-^^r. ^ slight posterior eraar- 

 gination on valves v/ith a de:?ided posterior production; umhones 

 tumid, high, prosog;;rate , area in front of the umbo slightly ex- 

 cavated; external surface v;ith conspicuous granules, ohscurely 

 arranged in radial seri , -ranules finer toward the poster- 



ior end; ligament area opisthodetic, narrow, flattened, extending 

 throu-^i.-j-.u the length of the posterior dorsal margin, poorly de- 

 fined on the left valve; chondrophore conspicuoiTS, placed "behind 

 the irmbo, directed towsrd the loosterior end, almost external on 

 the left valve; hinge with an obtuse rip-ht cardinal before the 

 chondrophore, a corresponding left deep, triangular soclret and a 

 long left posterior lateral, form.ed by the compression of the mar- 

 gin; interior of the valve subnacreous, v/ith obscure radii, the 

 ventrsl margin finely crenulated and the margin at the nosterior 

 end compressed. 



I)ir^:ensions .- Lat. V.5 mm.; alt., o.5 mm.; semidiam., S.5 mm. 



P^emarlrs .- -^'his species, which is v;eir i^esented, is recog- 



nized by its outline and granulation. Variation in outline is 

 apparent, come of the valves being slightly produced and roimded 

 posteriorly and others decidedly produced and subtruncated. ^he 

 YPlves that are most decidedly roiT'-de'" "oos'^^eriorly are us'zally 

 right valves and a concomitant feature is the lower and broader 



