250 
PALEONTOLOGY OF NEW-YORK. 
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 laminae 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, b. 
Orbicula squamiformis. Hall, Geol. Report, 1843, pag. 108, fig. 1. 
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 Orbiculce generally ; and it is probably identical 
with Patella? implicata of Murchison’s Silurian System, pag. 62, pl. 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. 
Pl. LII. Fig. 1 a-e. 
Reference Spiriferl pisum, Murchison, Sil. System, pag. 63, pl. 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 
