- 295 - 



--. Jhell small, moderatelj' inflcitel, decidedly' inequilateral, 

 sixbquadtate ; anterior margin rounding "broadly into the base, base 

 slightly curved and subpara'' "lei to the gently curved posterior 

 dorsal margin; posterior lateral margin scarcely roimded to obli- 

 quely subtruncate, joining the dorsal margin by a broad ciirve and 

 -leetiiig the ventral margin more abruptly; i:anbones almost anterior 

 in "Dosition, viell inflate'""', moderately.vn.de and high; limule small, 

 •^eeply im-nressed; external siirface sculptured with nineteen to 



twenty-tv.'o ribs bearing strong rounde'" -f-^"= ■'■t.^'^ e •-'^'^'ii°s; the 



first few anterior ribs separateri by wider interspaces; the suc- 

 ceeding :•'■ p to the posterior slope terraced on either side, 

 the nodulated -oortion formi.xg a rounded keel, -"'" '^ interspaces being 

 slightly narrov/er, beyond the T)OSterior slope tlie lov;er, terraced 

 portion of the rib becoming obsolete, the ribs reluced in ;vidth 

 and the interspaces co rresr)ond.ingly vrider; the last three poster- 

 ior ribs suddenly wider and bear nodules that are more compressed 

 at "^heir ends or even spinose and directed toward the posterior 



srgin; on the terrace:' ribs the nodii.les continuing across the 

 terraces as obscure \mdulations; very fine concentric st: ' -nd 



coarser, irregular concentric elevations also - resent on the terr- 

 :ces and in the interspaces; inner margin of the valve with very 

 short, coarse crenulations. 



Mrienfe i oa s . - lat. 19 mm.; alt. 19. E mm.; serai dia^.., 6.2 mm. 



