Maryland Geological Survey 181 



Occurrence. — Eomnky Foumatiox, Hamilton Member. West of iron 

 bridge over Town Creek northeast of Oldtown; on road east of Pine Hill 

 about 4 miles north of Oldtown. 



Collections. — Maryland Geological Survey; American Museum of Nat- 

 ural History. 



Family TEREBRATELLIDAE 

 Subfamily TROPIDOLEPTIINAE 



Genus TROPIDOLEPTUS Hall 



Tropidoleptus carinatus (Conrad) 



Plate XVI, Figs. 7-14 



Strophomena carinata Conrad, 1839, Third Ann. Rep. N. Y. Geol. Survey, 



p. 64. 

 Tropidoleptvs carinatus Hall, 1857, Tenth Rep., N. Y. State Cab. Nat. Hist., 



p. 151, figs. 1, 2. 

 Tropidoleptus carinatus Rogers, 1858, Geol. Penna., vol. ii, pt. ii, p. 828, 



fig. 672. 

 Tropidoleptus carinatus Hall, 18G7, Pal. N. Y., p. 407. pi. Ixii, figs. 2a-2r. 3a-.3p. 



3r-3M, 3w, 3x. 

 Tropidoleptus carinatus Keyes, 1891, Johns Hopkins Univ. Circ, vol. xi, p. 



29. 

 Tropidoleptus carinatus Hall and Clarke, 1893, Pal. N. Y., vol. viii, pt. ii, 



p. 304, figs. 227, 228, pi. Ixxxii, figs. 26-36. 

 Tropidoleptus carinatus Schuchert, 1897, Bull. U. S. Geol. Survey, No. 87, 



p. 457. 

 Tropidoleptus carinatus Clarke, 1903, N. Y. State Mus., Bull. 65, p. 344. 

 Tropidoleptus carinatus Grabau and Shimer, 1909, N. Am. Index Fossils, vol. 



i, p. 305, fig. 382. 



Description. — Shell concavo-convex ; outline generally semielliptical, 

 but the lateral margins are sometimes nearly straight and the front 

 broadly rounded; hinge-line equaling, greater or less than the width of 

 the shell, so that the cardinal extremities vary from rounded to mucro- 

 nate. "Ventral valve convex; broadly subcarinate along the middle, due 

 to the greater width and prominence of the central plication, and sloping 

 to the lateral margins and front. Cardinal extremities deflected ; average 

 width of cardinal area about 1 mm., the outer margin sloping toward the 

 extremities, the area striated longitudinally and divided by a broad, open 

 delthyrium. Dorsal valve varying from strongly concave to nearly flat. 



