- 195 - 



sculpture, relatively vade and forming a steep ledge on the left 

 valve; auricles subeqnal, v;ith weak radial ribs and fine concentric 

 lines; interior ventral marc'in deeply orentxlatea. 



■Dimensions ,- Left valve.- Lat. 50r:;m. ; al-^., 45 mm.; length 

 of hinge, 25 mm.; Ii-nmature right valve.- Lat., 52 ram.; alt., 



29,5 nui. ; diam. 7 "vm.; length of hinge aboixt 1!3 tmh. 



Remarks . - On the left valve the strong radial rihhing does 

 not terminate abruptly dorsally, the large ribs being followe*^ by 

 a few, weaker, closer radials, ?/hich gradually become obsolete 

 leaving the subm.arrins without radial sculpture. The dorsal m.ar- 

 -ins on the single m.ature left valve are proportionately shorter 

 than on the younger ones and more concave, ~hile the fine concen- 

 tric lines on the disk are not as prominent. ^'^■^.. ~ right valves 

 are proportionately less convex, vath lov/er and narrower ribs and 

 strone-er concentric sc ulpture which overrides the ribs. 



P. barretti is r ecor-nize'"' o^- its very convex right valve, v/ith 

 strong, almost square radial ribs and slightly concave left valve, 

 ?/ith equa"'ly strong, biit narrower anci square radials. It has been 

 confused with P. soror (nabb) (1) , described from Santo L'omingo 



(1). Trans. Amer. Philos, Soc, newser., vol. 15, v. 257, 1^73, 

 (as Jsnira soror). 



