CONTRIBUTIONS TO PAL^EONTOLOGT. 77 



This species differs in surface-marking from O. imhricatum of the Nia- 

 gara group, in the absence of intermediate finer longitudinal striae ; and 

 from O. virgatum, in the more regular distribution of the longitudinal and 

 stronger annulating striae. 



In two individuals of an inch and a half diameter, the portion of the 

 outer chamber preserved is nearly six inches in depth. 



Geological formation and locality. In limestone of the Upper Helder- 

 berg group : Williamsville, N.Y. 



ORTHOCERAS SUBULATUM. 



Orthoceras suhulatum -. Hall, Geol. Rep. 4th District New-York, 1843, p. 180. f. 1 



This species, characteristic of the Marcellus shale, occurs in 

 numerous localities, but usually in the form of casts. A single spe- 

 cimens from that rock, having the same proportions and flattened 

 at the larger extremity, is finely cancellated by longitudinal un- 

 dulating and transverse striae, which, at their junction, produce a 

 granulose or papillose surface. The transverse strise are more crowded 

 at regular intervals, and the surface is elevated in low ridges : this 

 feature is slightly perceptible in the casts. 



Geological formation and locality. In the Marcellus shale : Bloomfield ; 

 Avon ; Schoharie, and elsewhere. 



ORTHOCERAS CONSTRICTUM. 



Orthoceras constrictum : Vanuxem, Geol. Report Third District of New-Tork, 1842, 



p. 152, f. 1. 



This species is common in the coarser shales of the Hamilton group, east 

 of Cayuga lake. The specimens are not often larger than the one figured by 

 Mr. Vanuxem. The constriction occurs usually at a point one inch to one 

 and a half inches below the last septum : this feature is sometimes as ab- 

 rupt as represented in the figure cited. 



The siphuncle is small, central or very nearly so ; the septa comparative- 

 ly close, and very convex. There are apparently no surface-markings, except 

 fine transverse striae. 



A fragment where the diameter at the smaller end is a little less than 

 half an inch, has ten chambers in the length of an inch ; and another, of 

 larger diameter, has nine chambers in the same length. 



This species has a wide range. Specimens which do not difi'er in specific 

 character from those in New- York, occur in Maryland. 



Geological formation and locality. In the coarser shales of the Hamil- 

 ton group : at Cazenovia, Hamilton, and elsewhere in New- York ; and at 

 Cumberland, Maryland. 

 1861.] 



