striated, li:.dted "by a sharp -^p^'V'ia; sonie cTictance in front of the 

 posterior iiiargin on the ventral j)orti"on of the shell a poorlj^ -■''o- 

 finer", sli<?htli ir.:pressed a rea preserit, causing' tlie ventral t:--^'- 

 jrin to he feehl^ i*.-:".' '-'^ - ; ^- t'^^-i-i-^'l sciiLptnre of re "''■''■''•'"' I y 

 widely spaced lamellar con ;enl;rie rios, crenelated hy well-de- 

 fined radials extendiia,"; across the interepaces; the concen'^ric 

 ribs present on the limTi"^ f> , '"^""f" i'^ref^'--''^ 2rly crenulated, i:.::iediatel;^ 

 hehind the Imixile both racli&ls and the interspaces se];^rati)Tg them 

 relatively broad, to-rrard the center of the shell the radials re- 

 taining their -^ -ir? '■>i n-,- pl i" rr>,tT T- -.lo-,— 'nr-r-i-^ "J-.-i-f: -'r.V n interSpaCCS 



beo ming narrbvv:e.r, as the esciitcheon is approached the radials 

 rapidly becoming narrower, typically the concentric ribs ceasing 



abrr.^tly --^ ■''-'-• '^-■-•"■^ ■-<■: bounding ■"''^ e escutcheon; hinge normal, the 

 right ariterior eardiual interiial al crenrJations 



relatively coarse, 



Dinensiong ,- Lciigth, 21 mm.; alt., 19.6 rm. ; semicliam., 

 7 nm. 



Hemaric£.- The rather numerous valves of this species 



line. The ventral ly situatecl p- or depressed area aiid accom- 



panying emargination f the ventral Ria.ro-in in never conspicuous 

 on young shells is ^^p^'-it^ the ; -; '^^^ more -'--•-.-i- " -^^n 



"."'•^Its. There is also sorne variation in the proportion of length 

 to h...l.ht. One of tv70 of the broad anterior radials nay be med- 

 ially sulcate'-''. Occasionally the coneen-^ric ribs, '-''■■ ^^- -"■^ r^.n-.- 



