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 hut 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 cast 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 character and di¬ 
rection of the striae. 
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 boulders of the sandstone, which 
arc scattered over the southern counties of the State. 
Orthis miisculosa. 
Plate XCI. Fig. 1, 2, 3 ; and Plate XCV. Fig. 1-7. 
Orthis 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 great 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 ven r slight marks 
of trilobation on the summit : brachial lamellae broad and strong, and 
separated from the shell on each side by deep dental fossets. 
[ Palaeontology III.] 52 
