MARYLAND GEOLOGICAL SURVEY 347 



slightly concave; hinge area rather narrow, not massive; muscular im- 

 pressions and pallial margin very distinct. 



Length, 88 mm.; height, 47 mm.; diameter, 15 mm. 



Occurrence. — Calvert Formation. Fairhaven, Lyon's Creek, Chesa- 

 peake Beach, 3 miles south of Chesapeake Beach. Plum Point, Church 



Hill. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 



U, S. N'ational Museum. 



Crassatellites marylandicus (Conrad). 

 Plate XCIII, Figs. 1, 2, 3. 



Crassatella Marylandica Conrad, 1832, Fossil Shells of the Tertiary, p. 32, pi. viii, 



flg. 1. 

 Crassatella Marylandica Conrad, 1838, Fossils of the Medial Tertiary, p. 21, pi. xii, 



flg-. 1. 

 Crassatella Marylandica Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 578. 

 Crassatella marylandica Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), 



p. 7. 

 Crassatellites (Scambula) marylandicus Dall, 1903, Trans. Wagner Free Inst. Sci., vol. 



ill, pt. vi, p. 1473 (in part). 



Description. — " Ovate oblong, thick and ponderous; posterior side nar- 

 rowed and produced, with the extremity angular or obtusely rounded; 

 umbonial slope subangular; inner margin entire." Conrad, 1832. 



Shell convex; umbo elevated and prominent; regular concentric undu- 

 lations on umbonal slope very slightly developed or obsolescent; surface 

 marked by somewhat irregular growth lines; posterior basal margin 

 often slightly emarginate ; posterior and dorsal slopes meet in an angular 

 line or ridge; posterior slope crossed by a slightly obtuse ridge extending 

 from the beak to the upper end of the obliquely truncated posterior 

 margin; posterior dorsal margin deeply concave, anterior one straight; 

 hing^ area broad ; teeth robust ; muscular impressions deep ; pallial line 

 distinct. 



The young are convex, thick and massive also, with prominent beaks 

 and but slightly produced posterior extremity, giving the shells a 

 triangular outline. The regular, concentric undulations on the umbonal 

 slope are small and not profound and are confined to the portion of the 

 surface in the immediate vicinity of the umbo. 



