NIAGARA GROUP. 



291 



655. 32. ORTHOCERAS {Species undetermined). 



PL, LXI. Fig. 3. 



A fragment of a shell, apparently an Orthoceras, with strong, projecting, undulating, and 

 imbricating laminse. It belongs to a species otherwise unknown at this period. 

 Position and locality. In the limestone of this group at Rochester. 



656. 33. ORTHOCERAS IMBRICATUMI 



Pl. LXI. Fig. 4 a, &, c ; and Pl. LXII. Figs. ], 2, 3. 



Compare Orthoceratites imbricatus, Wahlenberg, Acta Soc. Sci. Upsal. 1827, p. 89. 



" — — HisiNGER, Petref. Suecica, 1837, pag. 29, pl. ix, fig. 9. 



" Orthoceras imbricatum, Sow. in Murchison, Sil. System, pag. 620, pl. 9, fig. 2. 



Cylindrical'? gradually tapering ; septa distant one-third to one- fourth the diameter, four to 

 eight in the space of an inch ; surface annulated at the septa. 



All the specimens seen of this species are flattened, and the shell partially or entirely re- 

 moved. The cast of the interior shows a projection at the septum ; and the interior of the shell, 

 which is seen in another specimen, shows a depression at the same point. Specimens from 

 which the shell is removed are covered with minute flustroid corals, of various species, one of 

 which is figured on Plate 40 E, fig. 6 a, 6, page 172 of this volume. 



In the compressed specimens the septa are oblique or undulating ; but this probably arises 

 from pressure, since in the fragment of a cast (fig. 3, pl. 62) which is less compressed, the 

 septa appear regularly arching. 



Fig. 4 a, b, c. Fragments of small individuals of this species. The surfaces of the cast are marked 



by the presence of minute corals. 

 Plate Ixii. fig. 1. A compressed cast of a large individual, the surface of which is marked in like 



manner by corals. 

 Fig. 2. The interior of the shell of a large specimen of this species. 

 Fig. 3. A fragment of a large specimen which is less compressed than usual. 



The septa in this species are often unequally distant, or there appears to be an intercalated 

 septum. 



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



657. 34. ORTHOCERAS VIRGATUM'? 



Pl. LXIII. Fig. 2 a, b, and fig. 3. 

 Compare Orthoceras virgatum, Sow. in Murchison, Sil. System, pag. 622, pl. 9, fig. 4, 

 Also 0. angulatum, Wahlenberg, 1. c. p. 9 ; Hisinger, Pet. Suecica, p. 28, t. x, f. 1. 

 And O. canaliculatum. Sow. in Murchison, Sil. System, pag. 632, pl. 13, fig. 26. 



Very gradually tapering ; surface marked by longitudinal angular ridges, which are arranged 

 at unequal distances, or with smaller ones intercalated. 



