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PALEONTOLOGY OF NEW-YORK. 
the middle : mesial elevation rounded, moderately prominent. Foramen 
narrow, the margins exsert. 
Surface marked by four, five, or six rounded or obtusely angular plica¬ 
tions upon each side of the mesial fold and sinus, concentrically 
marked by fine closety arranged granulose lamellae, which are strongly 
arched upon the central plications. 
This species, in its surface markings, resembles S. cycloptera and S. crispus; but 
the lamellae are more closely arranged, and the plications are subangular or less 
broadly rounded than in those species : the character and proportion of the area 
and foramen are likewise quite different. 
Fig. 2 a, b, c. Dorsal, ventral, and profile views of the same specimen. 
Fig. 2 cl, c. Cardinal and front views of the same. 
Fig. 2/. Enlargement of the surface. 
Geological position and locality. In the shaly limestone of the Lower Heidelberg 
group : Becraft’s mountain near Hudson; and Decatur county, Tennessee. 
Spirifer tenuistriatas (n. s.). 
Plate XXVIII. Fig. 3 a - d. 
Shell subrhomboidal, length and breadth about equal; cardinal extremi¬ 
ties rounded : valves about equally convex ; hinge line less than the 
width of the shell. Ventral valve much longer than the dorsal, greatest 
convexity nearly opposite the hinge line, much elevated towards the 
umbo, with the beak abruptly incurved over the foramen : sinus shal¬ 
low, curved above, and becoming flat in the bottom towards the base. 
Area not strongly defined, high, not exceeding half the wudth of 
the shell. Dorsal valve semielliptical, most convex in the middle : 
mesial fold broad, rounded, prominent towards the front. 
Surface marked by five or six depressed rounded plications upon each 
side of the mesial fold and sinus, and which become gradually obsolete 
towards the margin of the shell; the entire surface covered by ex¬ 
tremely fine radiating striae which are scarcely visible to the naked 
eye, and these are crossed by finer concentric striae which crenulate 
the radiating striae. 
