314 SYSTEMATIC PALEONTOLOGY 



more projecting and more acute beak, is somewhat more acutely tri- 

 angular in outline and within has a much more massive cardinal area 

 and larger teeth. 



Length, 40 mm. ; height, 34 mm. ; diameter, 12 mm. 



Occurrence. — St. Mary's ForaiATiON. Cove Point, St. Mary's Eiver. 

 Choptank Formation. Jones Wharf, Peach Blossom Creek. 



Colleciion. — Maryland Geological Survey. 



Genus CYTHEREA Bolton. 

 Subgenus ANTIGONA Schumacher. 



Cytherea (Antigona) staminea Conrad. 

 Plate LXXVI, Figs. 6, 7, 8. 



Cytherea staminea Conrad, 1838, Fossils of the Medial Tertiary, p. 46 (name only). 

 Cytherea staminea Conrad, 1839, Fossils of the Medial Tertiary, cover of No. 1, p. 3, 



pi. xxi, fig. 1. 

 Dione staminea Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 575. 

 Dione staminea Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 10. 

 Artena staminea Conrad, 1871, Amer. Jour. Conch., vol. vi, p. 76. 

 Venule (Artena) staminea Whitfield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 73, pi. 



xiii, tigs. 3-10. 

 Cytherea (Artena) staminea Dall, 1903, Trans. Wagner Free Inst. Sci., vol. iii, pt. vi, 



p. 1279. 



Description. — " Shell subtriangular, thick, with about ten very promi- 

 nent acute slightly reflected concentric ribs, with an intermediate carina, 

 and crowded minute lamellar striae; anterior tooth very small; margin 

 crenulated. Length 1 inch." Conrad, 1839. 



Form compact, rounded, triangular; valves convex; beak not promi- 

 nent; ribs perpendicular to the surface and at times as many as sixteen; 

 posterior edge of dorsal slope often marked by a slight ridge causing a 

 slight posterior basal emargination ; cardinal teeth three in each valve; 

 anterior lateral tooth in left valve very small and rounded and fitting into 

 a correspondingly small socket in right valve ; muscular impressions sub- 

 equal ; pallial sinus a mere notch. 



Length, 27 mm. ; height, 22 mm. ; diameter, 8.5 mm. 



Occurrence. — Calvert Formation. Chesapeake Beach, 3 miles south 

 of Chesapeake Beach, Plum Point, Lyon's Creek, Eeed's, Church Hill. 



Collection. — Maryland Geological Survey. 



