384 SYSTEMATIC PALEONTOLOGY 



FoRMATiox. Church Hill, 3 miles west of Centerville, Chesapeake 

 Beach, Plum Point, Hollin Cliff, Eeed's, White's Landing. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. jSTational Museum, Philadelphia Academy of Xatural Sciences. 



Family PINNID/E. 



Genus ATRINA Gray. 

 Atrina harrisii Dall. 

 Plate cm, Figs, 2, 3. 



Atrina ITarrisn Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, p. 663, 

 pi. xxix, fig. 11. 



Dcscriftion. — " Shell rather thick (the fibrous layer lost in the speci- 

 mens), ovately rounded behind, moderately convex; hinge line straight, 

 ventral margin slightly incurved; the surface of the pearly layer shows 

 the dorsal region with numerous fine longitudinal elevated lines, belovV 

 which the shell is at first nearly smooth, then the ventral region is 

 sculptured with numerous close-set concentric ril)lets. Length of por- 

 tion preserved about 150, max. width 60, diam. 32 mm." Dall, 1898. 



More perfect specimens show the hinge line to be slightly convex; 

 the fine lines dorsallv become obsolete toward the posterior end, the 

 prismatic layer there showing only faint irregular concentric growth 

 riblets that become stronger on the ventral slope; prismatic layer thin; 

 ventral margin thickened and angularly incurved. 



Length, about 170 mm. ; width, 85 mm. ; diameter, 28 mm. 



Occurrence. — Choptank Formation. Pawpaw Point, Jones Wharf, 

 Calvert Formation. Plum Point, Truman's Wliarf, Chesapeake 

 Beach, White's Landing. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum, Philadelphia Academy of Natural Sciences. 



Atrina piscatoria n. sp. 



Plate CIV, Fig. 1. 



Description. — Pearly layer of shell thin, prismatic layer thick; moder- 

 ately convex, rounded posteriorly; hinge line nearly straight; ventral 

 margin incurved; ventral and dorsal margins forming an angle of about 



