ORISKANY SANDSTONE. 409 



PLATE XC. 



Fig. 1. Cast of the dorsal valve of a younger specimen than that of the preceding plate. 



Fig. 2. Cast of the ventral valve of a specimen of medium size, showing the lower part of 

 the muscular impression but faintly defined. 



Fig. 3. A similar specimen, which preserves a portion of the shell. 



Fig. 4. An older shell, in which the cast is very perfectly preserved. 



Fig. 5 & 6. The interior and the east of a very old shell. 



Fig. 7. A portion of the surface striae enlarged. 



PLATE XCI. 



Fig. 4. The cardinal area, showing the closed foramen. 



Fig. 5. A portion of the surface of a young shell enlarged, showing the ohapaoter and di» 

 rection of the striaj. 



PLATE XCIV. 



Fig. 4. The cast of the dorsal valve of a young shell of this species, 



Geological position and locality. In the Oriskany sandstone : Albany and Scho- 

 harie counties ; and along the outcrop of this rock through Herkimer, Oneida and 

 Onondaga counties. It is likewise often found in bouldefs of the sandstone, which 

 arc scattered over the southern counties of the State, 



Ortliis niusculosa. 



Plate XCI. Fia. 1, 2, 3 ; and Plate XCV, Fiq. 1-7, 



Orihix musculosa : Hall, Annual Report of the Regents of the University upon the State Cabinet of 

 Natural History for the year 1856 (published 1857), p. 46; Palaeozoic Fossils, 1857, p. 6. 



Shell suborbicular, the length about nine-tenths as greq,t as the width. 

 Ventral valve depressed-convex, sometimes slightly concave near the 

 front : beak prominent, equalling or extending a little beyond that of 

 the opposite valve, pointed and slightly incurved : hinge extremely 

 short ; area triangular, extending little beyond the foramen ; foramen 

 large, partly occupied by the prominent cardinal process of the other 

 valve : dental lamellae strong and prominent, continued below in the 

 elevated margin of the muscular impression, which is large, fan-shaped, 

 and strongly marked. Dorsal valve regularly and distinctly convex, 

 most elevated in the central region, sometimes a little flattened or 

 depressed towards the front : beak prominent, triangular, pointed and 

 incurved ; cardinal process large, and sometimes with verj" slight marks 

 of trilobation on the summit : brachial lamellaa broad and strong, and 

 separated from the shell on each side by deep dental fossets. 

 [ Pal^ontolooy III.] 52 



