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118 PAL^ONtOLOGV OF NEW-YORK. 



Position and locality. This species occurs in every part of the Trenton limestone, ap- 

 pearing near its base, and continuing throughout : it also appears in the Hudson-river 

 group, in almost equal numbers. (State Collection.) 



166. 3. ORTHIS SUB^EQUATA. 



Vu XXXII. Figs. 2 a, J, e, d, e,f. 



Orthii sukctquata. CoimAD, Proc. Acad. Nat Sci. Philadelphia, 1843, Vol. i. p. 333. 



Compare Orthis parva, var. avellana. Vebnevu., Pal. Russia & Ural Mountains, 1845, p. 188, 1 13, f. 3 & 4. 



Semioval or subglobose ; length and breadth about equal ; valves ventricose, subequal, 

 regularly rounded in front ; cardinal line about equal the width of the shell ; area rather 

 large ; dorsal valve very convex, with a prominent elevated centre ; beak extended, 

 ■carcely incurved ; ventral valve regularly convex, with scarcely a depression in the centre ; 

 surface covered with crowded, radiating, nearly equal striae. 



Length f\ of an inch ; breadth a little greater. 



This shell bears some resemblance to the 0. testudinaria, but differs in the nearly equal 

 convexity of the valves, the larger area, and more crowded striae, which do not exhibit the 

 fine concentric lines of the latter species. Well defined specimens have not been found in 

 New- York : the one figured is from the Collection of Mr. Conrad. From its general re- 

 semblance to 0. testudinaria, it would be easily overlooked ; and since it occurs in the same 

 association at the West, it is not improbable but it will be found in New- York. 



Fig. 2 a. Ventral valve, showing the projecting beak of the dorsal valve, and a portion of the cardinal 



area and foramen, which is a narrow slit extending to the beak. 

 Fig. 2 b. View of the dorsal valve of the same specimen. 



Fig. 2 e. Profile view of the same, showing the nearly equal convexity of the valves. 

 Fig. 2 d. Cardinal view of the same, showing a slight depression in the centre of the ventral valve. 

 ^igs. 2e,/ Figures of a smaller specimen; the ventral valve being less convex than in the older 

 «-.• specimen. 



Position and locality. 'This species occurs at Mineral Point (Wisconsin), in the Blue 

 limestone, associated with Lepttsna sericea, Orthis testudinaria, Delthyris lynx, and other 

 Trenton limestone fossils. 



167. 4. ORTHIS BELLA-RUGOSA. 



Pi- XXXI I. Figs. 3 a, b, c. 



Orthii bella-rugosa. Conhad, Proc. Acad. Nat Sci. Philadelphia, 1843, Vol. i. p. 33. 



Semioval ; length and breadth about as 7 to 8 ; valves almost equally convex \ ventral 

 valve with a narrow depression along the centre, which becomes indistinct towards the 

 margin ; beak of the dorsal valve considerably extended beyond the cardinal line, scarcely 



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