57 Amhkican Kast Coast Arcas 57 



"Shell small, solid, oblique, witli prosogyrate beaks, somewhat impressed mesially 

 near the apices of the valves; right valve ovate-rhombic with twenty strong, rounded, 

 nodulous, radial ribs, separated by wider interspaces; left valve decidedly smaller, witli 

 the ribs smooth, squarish, and without nodules, except a few on some of the shorter an- 

 terior ribs; cardinal area wider in front of the beaks, narrower behind them; margins of 

 the valves internally fluted; hinge-line short, with about twenty-two subequal vertical 

 teeth. Lon. (of left valve) 5, alt. 4.7, diam. 5 mm. 



"This little shell was at first thought to be the young of a larger species, but noth- 

 ing allied to it of a larger size has turned up at any locality in the formation, while its 

 solidity gives it a mature appearance. The cardinal area differs in form from any of the 

 known species in the adult state." — Dall, 1898. 



Evidently the words right and left are interchanged in the original description. 

 More than half of the ligament lies behind the beaks and it does not cover the entire 

 cardinal area, but leaves a broad, uncovered band along the anterior and posterior mar- 

 gins of the cardinal area. There is no sulcation parallel to the umbonal ridge as in A. 

 incongnia . 



Ditnensions. — (Left valve), lon.+2.s,-4; alt. + 1,-4. 5; semidiam. 3 mm. 

 Ocairrence. — Oligocene of the Chipola beds, Chipola River. Florida. — Dull. Oligo- 

 cene of Sour Lake, Texas. — C. U. Mitf^eum. 



Area scalaris Conrad 

 Plate XIII, Figures 10, 11 



A)ia scalaris Conrad, Acad. Xat. Sci. I'liila., Proc. for 1843, p. 324, 1.S43. 



Area scalaris Conrad, Fos. Med. Tert., p. 59, pi. 31, fig. i, 1845. 



Ajra scalaris Tuomey and Plolmes, Pleiocene Fos. S. Car., p. 43, pi. 16, figs, i, 2, 1856. 



Scapharca [Area) scalaris Conrad, Acad. Nat. Sci., Phila., Proc. for 1S62, p. 580, 1S63. 



Scapharca (Cunrarca) scalaris Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 634, 1898. 



"Obliquely rhomboidal, elevated, ventricose, ribs about twenty-three, broad, square, 

 prominent, profoundly and robustly crenate, wider than the interstices, seven on the pos- 

 terior slope, prominent; posterior slope flattened; umbonial slope angulated; simimit 

 elevated, narrowed; anterior margin obliquely truncated; anterior basal margin obliquely 

 sub truncated; posterior extremity subangulated; beaks remote; area with transverse 

 slightly impressed lines; cardinal teeth irregular, oblique towards the extremities of the 

 hinge line; within with furrows corresponding to the ribs; margin profoundly crenate. 

 Length two inches: height, one and a half inches * "'' *. 



"Allied to A. incongr^ia Say. The description applies to the left valve only as the 

 opposite one has not yet been found." — Conrad, 1843. 



/>/;«f«.ww.? (Small left valve). — Lon. -4-12,-15; alt.-|-4,-2o; semidiam. 10 mm. 



Occurrence. — Darlington District, South Carolina. — Tuomey and Holmes. Miocene 

 of Petersburg, Virginia; of Duplin County, North Carolina, and of the upper bed at 

 Alum Bluf?, Florida. — Dall. Miocene of North and South Carolina (young) , and of Pe- 

 terslmrg, \"irginia.- -C l^. Musniw. 



