ORISKANY SANDSTONE. 
421 
The interior of the ventral valve shows strong dental lamellae, which 
are curved backwards beneath the area, and do not extend so low on the 
shell as its lower margin. Muscular area not defined in the specimen 
examined. 
This species resembles the S. cycloptera of the Lower Helderberg group; and it 
may be only a variety of form, resulting from a change of conditions in the sedi¬ 
ment. The proportions are usually somewhat different, and the area is higher than 
in that species. 
Fig. 8 a, b. Ventral and dorsal views of a specimen of ordinary size. 
Fig. 8 c. Front view of a specimen which is less gibbous than usual. 
Fig. 8 d. Profile view of a more gibbous specimen. ( The dorsal valve is represented as too 
convex.) 
Fig. 8 e. An enlargement of the surface, showing the fine concentric and radiating striae. 
Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 
\ 
Spirifer cnuiberlandise. 
Plate XCVI. Fig. 9 a-g. 
Spirifer cumberlanditR : Hall, Regents’ Report of 1856, p.63; Palaeozoic Fossils, 1857, p. 23. 
Shell broadly semicircular; valves moderately and nearly equally con¬ 
vex. Ventral valve regularly convex-; mesial sinus narrow, shallow, 
and flat in the middle : beak gently incurved, and projecting slightly 
beyond the hinge-line; area broad, nearly flat, parallel with the axis 
of the shell; foramen somewhat large, often partially or entirely closed. 
Dorsal valve having a narrow flattened mesial fold, convex in the 
middle, and flattened towards the extremities : beak scarcely incurved, 
and nearly in the same plane with the cardinal margin ; hinge-line 
straight; extremities extended. 
Surface marked by fourteen to seventeen simple rounded costae, which 
are crossed by concentric elevated lines or lamellae. 
The muscular impressions in the ventral valve are well defined and 
distinctly striated longitudinally, with a broad median ridge, which, in 
its upper part, is marked by a narrow central crest. The dental lamellae 
