392 SYSTEMATIC PALEONTOLOGY 



Length, 20 mm.; height, 12 mm.; diameter, 6 mm. 

 The Virginia specimens are often twice these dimensions or larger. 

 Occurrence. — Choptank Formation. Jones Wharf. Eare and 

 small. Calvert Formation. Church Hill, Fairhaven. 

 Collection. — Maryland Geological Survey. 



Section CALLOARCA Gray. 



Arc A (Barbatia) marylandica Conrad. 

 Plate CVI, Fig. 7. 



Byssoarca marylandica Conrad, 1840, Fossils of the Medial Tertiary, p. 54, pL xxix, 



fig- 1- 

 Barbatia Marylandica Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. .580. 

 Barbatia marylandica Meek, 1864, Miocene Check List, Smitb. Misc. Coll. (183), p. 6. 

 Barbatia Marylandica Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 48, pi. vii, 



figs. 2-4. 

 Barbatia {Calloarca) marylandica Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, 



pt. iv, p. 633. 



Description. — " Shell oblong, compressed, thin, with very numerous 

 radiating granulated striae; beaks not prominent; base much contracted 

 or emarginate anterior to the middle; posterior side dilated, the superior 

 margin very oblique and emarginate; extremity angulated, and situated 

 nearer to the line of the hinge than to that of the base; cardinal teeth 

 minute, except toward the extremities of the cardinal line where they 

 are comparatively very large and oblique; inner margin entire." Con- 

 rad, 1840. 



It may be readily identified by its general shape, or when found in 

 fragments, as is usually the case, by the granulations of the striiic. 



Length, 30 mm. ; height, 27 mm. 



Occurrence. — Calvert Formation. "Cliffs of Calvert" (Conrad), 

 3 miles west of Centerville, Plum Point, Centerville. 



Collections. — Maryland Geological Svirvey, U. S. National Museum. 



Section GRANOARCA Conrad. 



Arca (Barbatia) Virginia Wagner. 

 Plate CVI, Fig. 8. 



Area virginice Wagner, 1839 ? — See Dall, below. 



Arca virginice Bronn, 1848, Hand. Gescb. Nat., Index Pal., pt. i, p. 99. 



Arca virginice Bronn, 1849, Hand. Gescb. Nat., Index Pal., pt. ii, p. 283. 



