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ARGA (S3AHL12CA) PP.EPKAim n. sp. 



Aroa ( Scaoliarca ) aiirioula ta Lamarok ?, Dall, 1898? Trasas. V/agner 

 Free Inst. Sci., Philadelphia, vol. 5, pt. 4, p. 649. 



Description .- "^hell of merlitun size, decidedly inflated; post- 

 eriorly the angle hroadly prc^ucefl and the raarrin slightly insinu- 

 ated near the dorsal angle; anterior margin romKling by a broad 

 curve into the gently and asyimnetrically arcimte base; both extre- 

 mities of the" straight dorsal margin angular; umbones medium height, 

 full, prominent, at about the anterior third of the length; poster- 

 ior ridge strong, rounded, the posterior slope excavated; left 

 valve slightly lar -er, ^;7ith thirty-two, shai*ply chiseled, soixare 

 radial ribs separated by interspaces wider than the ribs in the ant- 

 erior and meciian portions of the shell, but narrower in the poster- 

 ior portion; in the anterior half of the shell the ribs diehotomoi:is 

 distally, on the posterior slope flatter and broader; all the ribs 

 except those on the posterior slope nodulated by numerous, sharp 

 concentric raised lines that persist across the intercostal s-naces; 

 right valve with thirty lower and broader radial ribs, the inter- 

 spaces being of about the same vadth in the anterior half of the shell 

 and narrower in the posterior half; only the anterior six or seven 

 ribs diehotomous, the nodulation United to the anterior ribs, the 

 nodules not as sharp as on the left valve; cardinal marprin of medium 



