6 * The Faujta of the Keysek Member of the 



below the beak, gradually becomes wider and deeper, producing a deep 

 sinuosity or emargination in front. 



" The vascular area of the ventral valve occupies a comparatively 

 greater space than in shells of 0. ohlaia from the Helderberg, and it is 

 more elongated or triangular in form. In the dorsal valve, the double 

 imprints of the adductor muscles are well preserved." Hall, 1859. 



The forms collected in Maryland by the writer differ from those figured 

 by Hall in having the lateral margins well rounded ; giving to the shell a 

 much more circular appearance than the somewhat subtriangular outline 

 of those figured by Hall. 



Rhipidomella emargincda resembles somewhat Dalmanella quadrans and 

 Ddlmanella concinna but seldom assumes the subquadrate shape which 

 characterizes both these species. 



Length of average specimen about 1.5 cm.; width about 1.7 em. 



Occurrence. — Helderberg Formation-, Keyser Member. Keyser, 

 near Bloomfield, West Virginia; Cash Valley, Cumberland, Maryland. 



Collections. — Maryland Geological Surve}!-, U. S. National Museum. 



Superfamily STROPHOMENACEA 

 Family STROPHOMENIDAE 



Genus LEPT/€NA Dalman 



Lepivena rhomboidalis (Wilckens) 



Plate LVI, Figs. 13-17 



Concliita rhomhoidalis Wilckens, 1769, Nachriclit von' selten Versteiner- 



ungen, p. 77, pi. viii, figs. 43, 44. 

 LepUcna depressa Hall, 1852, Pal. N. Y., vol. ii, p. 257, pi. lili, figs. 6a-6Z. 

 Strophomena rugosa Hall, 1859, Pal. N. Y., vol. ill, p. 195, pi. xix, fig. 1. 

 Leptcvna rhomboidalis Hall and Clarke, 1892, Pal. N. Y., vol. viii, pt. i, 1892, 



p. 279; pi. viii, figs. 17-31; pi. xva, figs. 40-42; pi. xx, figs. 21-24. 



Description. — " Shell semioval or semicircular ; hinge-line equal to or 

 extending beyond the width of the shell; dorsal valve having the upper 

 part nearly flat, slightly convex or even concave, with strong concentric 

 undulations, towards the margin abruptly inflected; ventral valve parallel 

 .to the dorsal valve, presenting a deep concavity. Surface marked by 

 prominent radiating striae. The cardinal area is narrow and extended to 



