348 SYSTEMATIC PALEONTOLOGY 



This species is likely to be confused in the adult stage with C. turgidulus, 

 with which it is doubtless closely related. For distinctions between 

 the two, see remarks under C. turgidulus. 



Length, 84 mm.; height, 57 mm.; diameter, 17 mm. 



Occurrence. — Choptank Formation. Governor Run (upper bed only), 

 Flag Pond (upper bed only). Turner, Peach Blossom Creek, Dover 

 Bridge. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

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



Crassatellites turgidulus (Conrad). 

 Plate XCII, Figs. 3, 4, 5. 



Crassaiella turgidula Conrad, 1843, Proc. Acad. Nat. Sci. Phila., vol. i, p. 307. 

 Crassatella turgidula Conrad, 1845, Fossils of the Medial Tertiary, p. 69, pi. xxxix, 



fig. 7. 

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

 Crassatella turgidula Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 7 

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



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



Description. — " Oblong-ovate, sliglitly ventricose; surface with coarse 

 lines of growth, and concentric undulations obsolete except on the um- 

 bones, where they are strongly marked and wide; beaks submedial; um- 

 bones flattened; anterior dorsal margin straight; posterior extremity 

 truncated and nearly direct, more oblique in young shells; basal margin 

 swelling a little anteriorly, posteriorly straight to the extremity which 

 is obliquely angulated." Conrad, 1843. 



Shell thick, convex, and not strongly produced posteriorly; umbo not 

 prominently elevated; posterior dorsal margin slightly concave or nearly 

 straight; hinge area broad; teeth robust; muscular impressions deep; 

 pallial line distinct. 



The young are long-ovate in outline, thin and flat; surface with very 

 prominent, regular, angular, concentric undulations on the umbonal 

 slope and extending over a large portion of the entire surface of the 

 shell; posterior dorsal margin straight or convex. 



This species is likely to be confused with C. marylandicus, but may be 

 separated in the adult stage by having a less prominent, broader, and 

 more flattened umbo and a more profoundly and widely undulated um- 



