- 'Uj - 



subtrimcated 'belo'.v, meeting tho l-jaae at an an^le o :" abor.t 90'^; \m\- 

 "bones tiimid., relatively "hig'h. aiid narrov/; -posterior carina otrori';-, 

 suTDangu.lar ; upper portion of the depressed posterior area elevat- 

 ed; p- tf^rnal siTfaoe s eiilpt itt e rl m'tii -hT-n" -,--f;- _-*:■' -i^o fortj- lov;, 

 subroiiiide-'l to • " d radial rios, separated u^^ narrower, sharp- 

 ie i'.'ijressed interspaces; the ribs and interspaces increasin-- in 

 size from the ant'^'-'^r e " '-o '^^ carina; t^^ r-^ic-'nt to ■'■f-->v, rii^s 

 behind the carina asymmetrically/ roitided, bein- " ^ ' overturn- 



ed toward the anterior end of the shell; luiv.orn snz'faces of the 

 ribs showing arohe''-, ffTT-Titi-, -nro ieoti-n o-^ ■,v-^-.'>row eon'^entrie bands 

 betv/een which are fiuei-, similarly? arche d s triae. 



Dimensions .- Lat., 28 mm.; alt., 54 ram.; semidiara., 13 ram. 



?.emar'-s . - Jeveral ■^-'^1^--,= - v'>i,:. _je identi..... i "^h recent 

 specimens of this long- ranging ki pec ies are present. 'Jhe ornament- 

 ation of t>>e ribs is usually intact on only a few small patches, 

 the ribs usually appearing polishes'' ^-■■•'^< ■'-i+'h ■^:'"''i oat ions of arched 

 incremental lines. If this siir "a-'e is removed both ribs and in- 

 terspaces are crosse'l by fine concentric striae, which, as usiial, 

 are arched on the ribs. 



The Bowden specimens ognized by the strong, straight 



carina, the presence of an elevate'^ area in the rteeply depresse'' 

 posterior region and the numeroiio hcixj-'J'.. rluo v/hich are ;.'eparat- 

 ed by v;ell- defined interspaces. .Tlien comparcl with certain fossil 

 c::-' recent forms of this s-pecics it is seen that the base is 



