52 



Palaeontographica Americana 52 



"Shell large, moderately thick, but slightly elongated, not inflated, with prominent 

 proscccElous beak; cardinal area wide, with numerous irregular, zigzag, longitudinal 

 grooves, bounded by a single deep curved groove from the beak to the ends of the hinge-line ; 

 hinge-line narrow; teeth small, obsolete medially, tending to become irregular at both 

 ends of the series; right valve with about thirty-one low ribs hardly as wide on anterior 

 dorsal slope as intervening spaces, broader and more elevated on posterior dorsal slope; 

 each rib mesially sulcated by a groove with one or more subordinate grooves on either 

 side; growth lines distinct; margin a continuous curve from anterior end of hinge line to 

 posterior end of base, there sharply curved; posterior margin oblique to hinge line; in- 

 terior margin crenulated ; dorsal and posterior slopes meet in an angle that becomes 

 rounded near the basal margin. 



"This species seems to be intermediate between A. staminea and A. subrostrata, 

 being perhaps more nearly related to the latter. 



"Length, 60 mm.; height, 48 mm.; diameter, 22 mm." — Gloui, 1904. 



Occurrence. — Choptank Miocene of Jones Wharf, lower bed at Governor Run, 2 

 miles south of Governor Run, Maryland. — Glenn. 



Area clisea Dall 



Plate XII, Figures 7, 8 



Scapharca {Anadara) clisea Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 657, pi. 33, fig. 



25, 1S98. 

 Area (Scapharca) clisea Glenn, Maryland Geol. Surv., Miocene, p. 386, pi. 105, fig. i, 1904. 



"Shell large, heavy, inflated, short, with small, high, somewhat prosoccelous laeaks, 

 the two halves of the wide cardinal area inclined to one another in the adult at an angle 

 of about forty-five degrees; left valve ■with about thirty strong, flattened subequal radial 

 ribs with narrower interspaces; in the young the ribs are furnished with small trans- 

 verse nodulations, which graduall}' become obscure in the adult; the only transverse 

 sculpture is of the ordinary incremental lines; the ribs in the adult are flat topped and 

 rarel}^ show any tendency to mesial sulcation , and when present it appears only on a 

 few of the anterior ribs near the margin; the anterior end is obliquely rounded to the 

 base, the posterior end a little produced basally; the cardinal area is exceptionally wide, 

 with a single impressed line joining the beaks and six or seven concentric lozenges de- 

 fined by sharp grooves; a deep groove also bounds the area; hinge-line straight with 

 numerous small vertical teeth, becoming much larger distally and tending to break vip 

 into granules at both ends of the series in the senile shell. Lon. 51, alt. 53, diam. 

 S3 mm. 



"This shell is apparently related to A. calliplcura and A. staminea Conrad, and a 

 larger series of specimens may oblige us to unite all three as varies of a single species. 

 At present, however, the dift'erences seem too great to admit of this course. In A . cal- 

 lipleura the ribs are granulated and trijily sulcate, while in the present form they are 

 simple. A. clisea has no posterior truncation like that figured by Conrad in A. calli- 

 pleura. A.- staminea is more squareh' compressed before and behind, with a tendency 



