- 1' 



AROA (S3APHARGA) PZEPLSURA n. sp. 



Sesoription .- Shell of medium size, heavy, decidedly inflat- 

 ed, moderately inequilateral; "base gently and evenly rounded, sub- 

 truncated posteriorly, rounded anteriorly; ujnbones moderately high, 

 full, prominent, with an inconspicuous mer'ian suloation, situated 

 at about the anterior -fcird of the length; e:-ternal surface sculp- 

 tured with thirty-three high, flat-topped radial ribs of imiform 

 v;idth, separated by narrower dee pi; -channeled interspaces; on the 

 posterior slope the ribs lower and the interspaces v^rider than in 

 the othrr portions of the shell; concentric scul^^ture of fine, usu- 

 ally evenly space-^ raised lines, producing 1ot;v nodules on the ribs, 

 except on those on the posterior slope ; cardinal area moderately 

 "dde Vv'ith two ligament grooves behind the umbo; teeth numerous, 

 vertical, except at the posterior end, the series continuous; inner 

 margin with deep crenulations. 



Dimensions *- length, 23.5 mm.; alt., 17.5 mm.; semidiam., 

 9.6 mm.; length of hinge, 17 mm. 



Remarks.- A. t)erToleura is represented by two detached left 

 valves. It resembles most closely individuals of the sane size be- 

 longing to the soecies halidonata, but differs by being proportion- 

 ately more elorigate, heavier, less compressed in the posterior dor- 

 sal region,, more inflated and by having fuller, more prominent beaks. 



