306 SYSTEMATIC PALEONTOLOGY 



Description. — Shell solid, ovate cordate; beak curved well forward, not 

 very prominent; outer surface with close-set, concentric lamellai; lunule 

 marked, cordate; hinge area rather short, broad; cardinal teeth strong, 

 two in right valve strongly bifid ; posterior margin arched ; a broad, shal- 

 low impressed area or groove from beak to posterior margin just above its 

 point of meeting with the base; muscle impressions large and distinct; 

 pallial sinus acutely angular; inner margin crenulated. 



Length, 96 mm. ; height, 79 mm. 



Occurrence. — Cjioptank Formation. Governor Eun, Calvert For- 

 mation. Plum Point. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Venus plena (Conrad). 

 Plate LXXIX, Figs. 1, 2. 



Mercenarla plena Conrad, 1869, Amer. Jour. Conch., vol. v, p. 100. 



Venus Ducateli Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 67 (in part), pi. 



xi, figs. 4-7. 

 Ifercenaria plena Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 69, pi. xii, 



figs. 4-6. 

 Venus plena Dall, 190o, Trans. Wagner Free Inst. Sci., vol. iii, pt. vi, p. 1309. 



Description. — " Cordate, inequilateral, ventricose, oblique, with close 

 concentric rugose lines; posterior side subcuneif orm ; lunule ovate; inner 

 margin densely crenulated. 



"... It approximates M. capax Conrad, but is shorter, less ventri- 

 cose, more oblique; the hinge character differs, and the pallial sinus is 

 deeper and more angular." Conrad, 1870. 



In the type specimen the shell is rather thin and very convex or 

 vaulted. The posterior end is not blunted as in V. capax. The hmge 

 area in large specimens becomes broad and bears a striking resemblance 

 to that of 7. cuneata, as does also the general outline of the shell. It 

 may be only the immature form or a variety of V. cuneata. 



Length, 90 mm. ; height, 78 mm. ; diameter, 27 mm. 



Occurrence. — Choptank Formation. Governor Piun, 2 miles south 

 of Governor Eun, Flag Pond, Jones Wharf, Pawpaw Point, Peach Blos- 

 som Creek, Dover Bridge, "Eastern Shore" (Cope). Calvert For- 

 mation. Plum Point (Dall). 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 Academy of Natural Sciences of Philadelphia (type). 



