$22 PALEONTOLOGY OF NEW=YORK. 
Fig. 8 a. View of the ventral valve and area; the specimen imperfeet. 
Fig. 8 &. Interior of the dorsal valve, showing the cardinal area. 
Fig. 8 c. Exterior of the dorsal valve. 
Fig. 8 d. Interior of the ventral valve, showing the toothlike processes and visceral impression. 
Fig. 8 e. Profile view of a perfect specimen. 
This is a rare shell in New-York, and I have been able to obtain but few specimens, and 
these for the most part imperfect. Its associates in the strata are Orthis testudinaria, Leptene 
sericea, Altrypa triplex, Ceraurus pleureranthemus, §c. 
Position and locality. In New-York, it occurs in the lower part of the Trenton limestone, 
associated as above, at Middleville. It is found at Mineral Point ( Wisconsin ), apparently 
in the higher part of the same rock. (State Collection.) 
163. 10. ORTHIS PLICATELLA (xn. sp.). 
PL. XXXII. Figs. 9 a, b,c, d, e, f, g. 
Compare Orthis radians. J. SowErsy in Sil. System, pag. 639, pl. 22, f. 11. 
Broadly semioval, nearly equivalve, length and breadth about as 3 to 4; surface marked 
by strong radiating plice, which are usually simple, about 20 to 28 on each valve, crossed 
by simple elevated concentric lines, which are more distinct in the depressions between the 
coste, and often obscure or obsolete upon their exposed surfaces; valves nearly equally 
convex, without sensible depression or elevation on either one, meeting at the edges ina 
straight line; cardinal line not extending beyond the width of the shell; area narrow ; 
dorsal foramen extending to the beak. 
This species bears some resemblance to Orthis radians of SowERBY, but it proves clearly 
distinct on comparison with his description ; the plications are never so few as 15, and the 
shell is never concave in front. The equal convexity of the valves, and uniform, strong, 
somewhat sharp plications, are distinguishing characters. The proportionate greater exten- 
sion of the hinge line, and less distance from beak to base, distinguish this shell from any 
variety of O. pectinella, even when the surface only can be seen. 
Fig. 9 a. Ventral valve of medium size. 
Fig. 9 b. Ventral valve of a small individual. 
Fig. 9c. Ventral valve, showing the apex and part of the dorsal area. 
Fig. 9 d. Profile view of the same. 
Fig. 9 e. Cardinal view, showing the dimensions of the area and foramen. 
Fig. 9 f. Ventral valve of a large specimen ; the plications trifid towards the base. 
Fig. 9 g. Profile view of the same. 
Position and locality. A single well marked specimen only, has fallen under my observa- 
tion within the State (at Middleville), where it occurs in the lower part of the Trenton 
limestone. It is quite frequent at Cincinnati (Ohio), Maysville (Ky.), Madison (Indiana), 
associated with the Leptena alternata, L. sericea, Orthis testudinaria, and other fossils 
typical of the ‘Trenton limestone. (State Collection.) 
