CALCIFEKOtJS SANDSTONE. 13 



16. 1. ORTHOCERAS PRIMIGENIUM. 



Pi.. III. Figs. 11, 11 a. 



Orthoceras primigmia. Vanuxem, Geological Report, p. 2G, fig. 4. 



Elongated, terete, gradually tapering to an obtuse point; surface smooth?; section 

 circular ; septa thin, deeply concave, closely approximated, being distant only j'j the 

 diameter ; siphuncle 1 



In Mr. Vanuxem's figure, the septa are represented as about 4 or i the diameter. His 

 specimen presents a longitudinal section nearer the apex than mine, and therefore this 

 difference may be expected. The thin and closely approximate septa are very striking 

 characters, and will probably serve to distinguish this species. The parts usually preserved 

 in this rock are fragments near the apex, indicating that this portion was stronger than the 

 rest of the shell. 



Position and locality. This species is found in the higher calcareous portion of the rock, 

 in the Mohawk valley, near Fort-Plain, and also in abrecciated mass near the same place, 

 in great numbers. 



17. 2. ORTHOCERAS LAQUEATUM (n.ijj.). 

 Pl. III. Fig. 12. 



Somewhat rapidly tapering (to an acute point?); surface fluted, or marked by lon- 

 gitudinal angular ridges, with intermediate finer ones ; some faint remains of transverse 

 striae ; section circular. 



One or two only of the septa are still obscurely visible, regularly arched, but their 

 comparative distance cannot be ascertained. This fragment, being a portion near the apex 

 of the shell, is a part of what has been probably a much larger specimen. 



Position and locality. The position of the specimen is probably at the upper termination 

 of this rock, and just at its passage into the succeeding limestone. Its locality is uncertain. 



{State Collection.) 



In presenting these specimens as the typical fossils of this rock, it is not regarded as by 

 any means certain that they are exclusively confined to it. Since several of them occur 

 near its upper termination, and where the mass becomes more calcareous, it is not im- 

 probable they may appear again in the succeeding rock. The vegetable forms, however, 

 «o far as known, do not reappear, being apparently confined to the Calciferous sandstone, 

 and flourishing to its close, but disappearing with the augmentation of calcareous matter, 

 and giving place to the remarkable forms presented on Plates VIII. & IX. 



