ft 



250 rALvEONTOLOGY OF NEW-TORK. 



In the specimen fig. 1, there are a few longitudinal striae visible beneath the shell. The 

 specimen fig. 2 is proportionally broader and shorter than fig. 1, but there does not appear to 

 be sufficient difference to constitute a distinct species. 



Position and locality. In the shale of the Niagara group at Lockport, and at Rochester and 

 Sweden in Monroe county. 



610. 8. ORBICULA TENUILAMELLATA (n. sp.). 



PL. LIII. Fig. 3. 



Circular ; shell thin ; surface marked by prominent thin concentric laminae. 

 Imperfect specimens only have been seen, and the shell is extremely fragile. The thin ele- 

 vated laminjE are particularly characteristic of the species. 



Position and locality In the lower part of the limestone at Lockport. 



611. 9. ORBICULA'? SQUAMIFORMIS. 



PL. LIII. Fig. 4 a, 5, 

 , Orhiaila aquam^ormit. Hall, Geol. Report, 1843, pag. 108, fig. I. 

 Oval, very depressed, apex excentric ; surface marked by strong concentric lamellae, which 

 are close together on the anterior, but diverging on the posterior part of the shell. Shell thin, 

 translucent. 



This shell has a different appearance from the Orbiculx generally ; and it is probably identical 

 ■with Patella? implicata of Murchison's Silurian System, pag. 62, pi. 12, fig. 14 a. 



Fig. 4 a. An individual of the natural size. 



Fig. 4 b. The same enlarged, to show more distinctly the characters of the surface. 



Position and locality. In the shale, and upon the thin calcareous layers in the same, at 

 Lockport, and at Rochester and Sweden in Monroe county. 



612. 25. ORTHIS PISUM. 



Ph. Lll. Fig. la-t. 

 Reference SpiriferJ pisum, Murohison, Sil. Syatetn, pag. 63, pi. xiii, fig. 9. 

 Lenticular, globulose ; surface marked by fine concentric striae ; valves nearly equal, each 

 valve with a slight depression down the centre ; dorsal valve somewhat more convex, and the 

 beak more elevated than the ventral valve ; area narrow, small, scarcely extending beyond the 

 width of the beaks at their base. 



This fossil so closely resembles Spirifer pisum cited above, that I can scarcely doubt the 

 identity of the two. I have referred it to Orthis from its general form, from one valve being 

 smaller and somewhat flatter than the other, and from the narrow area which has so slight an 



