Maryland GiiJOLOGicAL Survey 129 



toward the front and sloping rather abruptly toward the lateral margins. 

 Surface marked by fine concentric striae and some coarser linos of growtli. 



This species somewhat resembles Lingula compta Hall and Clarke, but 

 that species is larger, neither so convex along the median line nor so 

 pointed at the extremities; also L. ligea Hall, but that species is larger, 

 wider in proportion to the length and not strongly convex along the 

 median line. This species apparently is readily distinguished from others 

 by its narrowness and strong median convexity. 



Length, 5^-8 mm. ; width, 2-1-4 mm. 



Famed in honor of Dr. William B. Clark, State Geologist of Maryland. 



Occurrence. — Eomney Formation, Hamilton Member. B. & 0. 

 E. R. cut at 21st Bridge. 



Collection. — Maryland Geological Survey. 



Superfamily DISCINACEA 

 Family DISCINIDAE 



Genus ORBICULOIDEA d'Orbigny 



Orbiculoidea lodiensis var. media (Hall) 



Plate Ylll, Figs. 14-17 



Orhicula lodensis Vanuxem, 1842, Geol. N. Y., pt. iii, p. 168, fig. 1. 

 Orbicula lodensis Hall, 1843, Geol. N. Y., pt. iv, p. 223, fig. 1. 

 Discina media Hall, 1863, Sixteenth Rep. N. Y. State Cab. Nat. Hist., p. 27. 

 Discina lodensis Hall, 1867, Pal. N. Y., vol. iv, p. 22, pi. i, fig. 14; pi. ii, fig. 35. 

 Discina media Hall, 1867, Pal. N. Y., vol. iv, p. 20, pL ii, figs. 25-29. 

 Discina media Walcott, 1884, Mon. U. S. Geol. Surv., vol. viii, p. 113. 

 Orbiculoidea lodensis Hall and Clarke, 1892, Pal. N. Y., vol. viii, pt. i, pi. iv F, 



fig. 21. 

 Orbiculoidea media Hall and Clarke, 1892, Pal. N. Y., vol. viii, pt. i, pi. iv E, 



figs. 15-17. 

 Orbiculoidea lodiensis media Schuchert, 1897, Bull. U. S. Geol. Surv., No. 87, 



p. 279. 

 Orbiculoidea media Clarke, 1903, N. Y. State Mus., Bull. 65, p. 268. 



Description. — " Shell broadly elliptical or subcircular, variable in form. 

 Dorsal valve very depressed-convex ; apex excentric, pointed, and inclined 

 towards the posterior border. Ventral valve flat, or a little convex Just 

 9 



