- 8" - 



portions of the shell (anterior to the umbonal depression high, 

 broad, sharply sculp tiired and separated by narro^^er interspaces; 

 in the v^ide depression verj- narrov:, lor/, and the v/ider inter- 

 spaces '.vith from one to four fine ^ary ribs that disappear 

 in the dorsal half of the shell; posterior to the depression the 

 ribs hiiiher and broader, '"ith one or two furrows, the equally wide 

 interspaces containine: fro ra two to five secondary ribs; the ribs 

 on the -oosterior keel very low and divided distally by furrows in- 

 to portions of irren-ulsr width; dorsal to the iTOsterior Veel the 

 first three ribs broad and usually furrowed, but the remainder 

 narrow), concentric sculpture of irregular groiAfth lines on both 

 the ribs and interspaces; cardinal area broad and long, the sub- 

 umbonal portion with discontinuous ligament grooves that diverge 

 at an acute angle; hinge long and straight; teeth numerous, becom- 

 ing longer and sli?"htly obliq::e distally; anterior and postetior 

 inner margins strongly crenulated, the ventral margin posterior 

 to the by s sal gape weakly crenulated. 



Di?:iensions .- length, 68 mm.; ma:^imum alt., 28 mm.; semidiam. , 

 15 mm. 



Rem.ar^:s .- "^he Bowden specimens, vtiich are nuraeroiis, agree 

 in every detail vdth the recent form of wide distribution in the 

 /intillean region. As is to be e::pected , from the habits of this 

 species, the sha-oe is variable with regard to details, but the 



