— ;Oii e_< — 



PSCTEiy (A3QUIPEGTEIT) ELA3HISTU3 n. sp. 



Sescrj-Qtion .- '^hell small, moderately inflate!, Buborbieiilar, 

 subequllateral; rip-ht vnlve nore inflateri +>,?,n '-lie left; exterior 

 siirfaee of right valve sculpt urer^ with tv/enty-one roimded or sub- 

 roiiided. radial ribs, separated by slightly narrower, roimded inter- 

 spaces; concentric sculptiire of fine, but conspicuou.s, concentric 

 raised lines, occasinnally overriding the ribs in the distal third 

 of the shell and in the same reg'ion rarely extended sufficiently 

 to form continuous concentric lines of slightly projecting, incon- 

 spicuous, thin, scales; left valve sciilpture " with seventeen or 

 eighteen strong, square radials separated by deeply impressed in- 

 terspaces of the same width, with the concentric lines usually prom- 

 inent in the interspaces and occasionally appearing on the ribs; 

 submargins , auricles and crura as in P. oxyonus. 



Dimensions .- A right valve: lat. , 10 mm.; alt., 10 mm.; 

 cliam. , 1.8 mm.; length of hinp-e, 5.5 mm.; A left valve: lat., 

 8.7 mm.; alt., T.S ram.; '^iara., 1.4 mm.; length of hinge, 5.9 vm, 



Rem.ark s . - P. elachistus . represente-'' by several valves, 

 all of which probably are not m.ature, closely resembles P. ox y genus 

 in general features, but the sculpture is decidedly different. 

 Right valves of elachistu:. have fewer, fone or two less) broader, 

 more rounded ribs, with correspondingly narrower interspaces, than 



