292 



PALJEONTOLOGY OF NEW-YOHK. 



The fragments of this species which have been obtained, give but an imperfect idea of the 

 entire shell. The only surface markings visible are the angular longitudinal ridges, which are 

 nearly <!qual and closely arranged in one specimen, and more distant and with smaller inter- 

 calated ones in the other. In neither of these specimens is there any visible transverse marking. 

 This differs from O. angulatum of Wahlenberg and Hisinger, in being straight, and in ta- 

 pering more gradually than in the figure given by the latter. In this respect it resembles more 

 nearly the 0. virgatum of Sowerby. The imperfection of the specimens, however, give no 

 means of deciding satisfactorily as to its specific identity or difference. 



Fig. 2 a. A fragment where the longitudinal ridges are equal and closely arranged. 



Fig. 2 b. A fragment enlarged. 



Fig. 3. A fragment where the longitudinal ridges attenuate in size. 



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



658. 35. ORTHOCERAS CANCELLATUM (n. s/j.). 



PL. liXIII. Fig. 1 and 4 a, b ; and Pl. LXV. Fig- 4 a, b. 



Cylindrical'? gradually tapering ; siphuncle? Surface marked by longitudinal angular ridges, 

 and intermediately by finer longitudinal stria; ; transversely marked by striae of equal size, 

 which, decussating with the longitudinal striffi, give the surface a cancellated appearance. 



The longitudinal ridges scarcely differ from those of the preceding species, but in that one I 

 have never been able to discover either longitudinal or transverse striiE between the ridges. 



Fig. 1. A part of a large individual, where the surface markings are scarcely preserved. The 

 stronger ridges have been worn down, and only fine strias are visible, except at a 

 single point, where the same characters are preserved as in 4 a and 4 b. 



Fig. 4 a. A small fragment, having the characters of the surface preserved in a tolerable degree 

 of perfection. 



Fig. 4 J. A portion of the same enlarged. 



Plate Ixv. fig. 4 a, b. An impression of the exterior of this species, in iron pyrites, in wliich the 

 sharp striae are well preserved. 



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



659. 36. ORTHOCERAS 



Pl. LXIII. Fig. 5. 



Several fragments of an Orthoceras, having fine transverse ridges or coarse strite, have 

 been found at Rochester. They approach in character to 0. imhricatum , but I have been unable 

 to decide upon their identity. 



