18G NEW YORK STATE MUSEUM 



carination and strongly backward curving lines of growth; and 

 B. pel ops [fig. 107] with a broadly rounded but keeled 

 periphery. 



The cephalopods are specially well represented in the Schoharie 

 grit, the orthoceratites being most characteristic. 



With the passage of this rock into a limestone (the Onondaga) 

 the occurrence of orthoceratites almost entirely ceases, at least in 

 the eastern part of the state. 



Notwithstanding the number of species, and the great number 

 of individuals, a very small proportion of the whole preserves the 

 surface markings. They are almost invariably in the condition 

 of casts of the interior, the shell having been dissolved by the 



Fig. 107 Bellerophon pel ops 



percolation of water through the coarse material of the rock. 

 In some examples, where the rock is less charged with arenaceous 

 [silicious] matter, the matrix adheres so closely, seemingly 

 cemented to the fossil, that no satisfactory evidence of surface 

 markings can be obtained. It is rarely possible to determine the 

 character or thickness of the exterior shell of the orthoceratites in 

 the Schoharie grit. The septa are extremely thin, often broken or 

 distorted, through the process of filling with sediment, while the 

 external form of the shell is preserved. The siphuncle, though 

 usually well marked in its passage through the septa, is rarely 

 to be found in the intermediate space, and, in the best examples, 

 is only partially preserved. Specimens which have been cut 

 longitudinally directly through the siphuncle, as shown on the 

 septa at the two extremities, preserve no evidence of that organ 

 in its passage through the chambers, and only a simple mark 

 or notch in the intermediate septa. We can account for this 

 absence only upon the supposition that the tube has been so 

 thin that its walls have been dissolved or broken away during 

 the process of filling the cavity with the surrounding sediment. 



