PLATE 47. 
Legend: d. Spondylium. s’. Median septum (brachial valve). 
b, Cruralium. D. Deltidium. 
s. Median septum (pedicle-valve). ce, Crura. 
PENTAMERUS, Sowerpy. 
Page 844. 
PENTAMERUS OBLONGUS, Sowerby. 
Figs. 1, 2. Dorsal and ventral views of a subquadrate shell with the lobation 
of the surface distinctly defined. 
Clinton group. Rochester, N. Y. 
PENTAMERUS OBLONGUS, var. SUBRECTUS, Hall. 
Fig. 3. Profile view of a normal mature individual. 
Niagara beds. Castle Grove township, Jones county, Iowa. 
PENTAMERUS OBLONGUS, Sowerby. 
Fig. 4. Dorsal view of a large, elongate, subovate shell, with trilobed surface, 
broadly shouldered umbones and closely incurved and depressed 
ventral beak. 
Fig. 5. A natural longitudinal section through both valves ; showing the com- 
paratively short median septum and septal plates, the projecting 
spondylium and crural processes. 
Clinton group. Rochester, N. ¥. 
Fig. 6. Dorsal view of the umbonal region of an internal cast in chert; show- 
ing the cavities left by the septum and septal plates, the deltidium 
and the lateral divisions of the hinge-plates. X 2. 
Niagara beds. Monmouth, Iowa. 
PENTAMERUS OBLONGUS, var. CYLINDRICUS, Hall and Whitfield. 
Fig. 7. Dorsal view of the original specimen of this variety; showing the 
elongate form and a faint trilobation of the exterior. 
Niagara group. Near Louisville, Kentucky. 
PENTAMERUS PERGIBBOSUS, Hall and Whitfield. 
Fig. 8. Profile of a small and gibbous internal cast. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
Fig. 9. Cardinal view of an internal cast of a small shell, which shows with 
much distinctness the position and form of the deltidium, 
Chert of the Niagara group. Wisconsin. 
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