374 CONTRIBUTIONS TO THE GEOLOGY OF 



the alternate ones nearly obsolete, dividing the costae into pairs; trans- 

 verse striae very minute ; hinge straight, area of ligament narrow, 

 with from three to four furrows; beaks small, somewhat incurved, 

 and not distant. Length four-fifths of the breadth, but these propor- 

 tions variable. 



Locality, King George county, Virginia, in the eocene, near the 

 Potomac river. 



Description. — The division of the costae into pairs, the great obli- 

 quity of the posterior margin, and its great breadth, are among the 

 characteristics of this shell. The area of the ligament rises from the 

 hinge at a more obtuse angle next the anterior side than at the poste- 

 rior, so that it curves upon an axis not coincident with the hinge line. 

 The transverse lateral teeth are very slightly oblique, they are on the 

 anterior side three, and on the posterior four ; fine acute grooves or 

 striae mark both sides of these teeth. The central longitudinal teeth 

 are few, irregular and rather oblique. The anterior and inferior mar- 

 gins of the right valve, especially, are strongly crenulated on the inner 

 edge. The anterior muscular impression is subtriangular and de- 

 pressed, the posterior one is nearly rectangular, the inner angle being 

 a little elevated. Shell moderately thick. 



Venericardia ascia. Plate XXIX., fig. 2. 



Specific character. — Shell subovate, subcordate, not thick; costae 

 much depressed except on the beak; about thirty; transverse striae 

 numerous from the margin to the umbones, nearly obliterating some 

 of the longitudinal sulci; lunule profound, subcordate, triangular and 

 equilateral ; anterior muscular impression rather remote from the 

 hinge; cardinal teeth arcuated, oblique; inferior and posterior margins 

 crenulated. Length, three inches two-tenths; breadth, three inches 

 six-tenths. 



Locality, King George county, Virginia, near the Potomac, in the 

 eocene. 



Hemarks. — This shell can be confounded only with the V. plani- 

 costa, to which it is possible we ought to refer it as a variety.. They 



