54 [ Senate 



StROPIIOMENA ( SlROrHODONTA) MAGNIVENTRA (U.S.). 

 Pal.N.Y. Vol.iii, pi. 92, f. 3. 



Shell subsemicircular varying to longitudinally suboval, variable j 

 length usually two -thirds the breadth, sometimes equal or 

 greater : ventral valve convex in the central and umbonial re- 

 gions, flattened towards the extremities ; beak slightly incurved ; 

 cardinal border sloping from the umbo : dorsal valve unknown, 

 probably concave : hinge-line crenulated, equal to the greatest 



" width of the shell, sometimes extended into mucronate points 

 beyond the lateral margins of the shell ; area of ventral valve 

 very broad, slightly curved, distinctly marked by vertical striae 

 produced by the prolongation of the crenulations of the hinge ; 

 foramen large, triangular, apparently mostly closed. Surface 

 marked by regular, rounded, slightly elevated, radiating striae : 

 interior scarcely granulose, strongly marked Avith a plicated 

 flabelliform muscular impression, covering nearly two-thirds of 

 its extent. 



This species is recognized in the casts ( its usual mode of occurrence in 

 the Orisliany sandstone) by the large and strongly marked vascular im- 

 pressions. 



Geological position and locality. In the Oriskany sandstone in Albany 

 and Schoharie counties. 



Stropiiomena ( Strophodonta) magnifica (n. s.). 



Pal.N.Y. Vol.iii, pi. 93, f.4; and pi. 95, f.l. 



Shell very large, transversely suboval, somewhat semicircular, 

 more or less rounded at the extremities of the hinge ; length 

 and breadth sometimes equal : ventral valve depressed-convex 

 in the middle and umbonial regions, flattened near the lateral 

 extremities ; cardinal margin sloping slightly from the beak : 

 dorsal valve slightly concave ; hinge-line crenulated, usually a 

 little less than the width of the shell -, area broad, distinctly and 

 regularly marked with transverse strise produced by the pro- 



