308 Systematic Paleoxtology 



marked than in the latter. The surface ornamentation is not well pre- 

 served, but the number of strife appear to be about as abundant as in 

 S. propinqua. 



This species is distinguished from ,S'. inultistnaia in being smaller, 

 less gibbous, and with coarser stria?. One example referred with doubt 

 to this species has a slight ventral fold and a narrow dorsal sinus, con- 

 ditions just the reverse of that in the other specimen regarded as the type 

 of *S'. orislania; otherwise the expression is that of Schizophoria. 



Length 1.8 cm. ; width 2 cm. 



Occurrence.— OmsKA:<!Y Formation, Eidgely Member. Cumberland 

 (Knobly). 



Collection. — George M. Boeder. 



Superfamily STROPHOMENACEA 



Family STROPHOMENIDAE 



Genus LEPT/€NA Daiman 



Lept.^na rhomboidalis (Wilckens) 



Plate LVI, Figs. 13-17 



Conchita rJiomboidalis Wilckens, 1769, Nachricht von selten Versteiner- 



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

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

 Strophomena rugosa Hall, 1859, Pal. N. Y., vol. iii, p. 195, pi. xix, flg. 1. 

 Leptwna 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 

 the extremities of the hinge-line; the foramen is broad and spreading, but 

 filled by a callosity of the ventral valve, which has a narrow groove at its 

 summit for the protrusion of the pedicle ; the apex of the dorsal valve is 

 often, and perhaps always, perforated. Tlie flatter portions of both valves 

 are strongly marked by concentric undulations, which are crossed by fine 



