466 GEOLOGY. 



it in notable abundance, as already remarked. Seventy species of 

 cephalopods are described from this fauna in New York alone. They 

 were particularly abundant in the Schoharie grit (p. 422), which occu- 

 pied the same district and had the same essential characters as the 

 Oriskany sandstone, which had been so barren of cephalopods. They 

 were also abundant in the calcareous tracts farther west, thus exhibit- 

 ing their relative independence of bottom conditions, as might be 

 expected of free-moving, predaceous animals. While the orthocera- 

 tites did not reach the gigantic dimensions of their Ordovician prede- 

 cessors, individually they attained fair sizes, three inches in diam- 

 eter being not uncommon. The club-shaped Gomphoceras appeared 

 in many large species, and the curved Cyrtoceras and Gyroceras were 

 abundant, while the closely coiled Nautilus was present but not abun- 

 dant. The ornamentation of the exterior was a notable feature, but 

 quite inferior to the elaborate ornamentation which it foreshadowed. 

 This prolific retention of old forms, combined with the introduction 

 of a new type, points apparently to some distinctive set of conditions 

 which distinguished the history of the Onondaga fauna, either in its 

 originating tract, or in its expansional stage, or in both. 



The persistence of the previous types of the gastropods and pelecy- 

 pods. — On the other hand, it is to be noted that the gastropods were 

 present in abundance and largely in the same peculiar facies that they 

 had assumed in the Helderberg and Oriskany faunas. As there, the 

 capulids were numerous, though perhaps less abundant. The acquisi- 

 tion of spines, which was initiated in the Oriskany fauna, became a 

 pronounced feature in this (Fig. 208, h), and perhaps signified that 

 there was occasion for defense, an occasion which either the fishes 

 or the cephalopods could doubtless have supplied. There were many 

 other forms of gastropods, including Euomphalus, coiled in a plane, 

 and Murchisonia, coiled in a very high spire. These, with the cap- 

 shaped capulids, filled out a full complement of gastropod types. 

 There was a notable similarity of the gastropods to those of the 

 Helderberg and Oriskany faunas, which seems to imply derivation 

 from them, in contrast with the peculiarities of the cephalopods which 

 seem to imply an origin from some other fauna. 



The pelecypods were also abundant and often resembled those 

 of the Helderberg and Oriskany from which many of them were 

 descended. .The large oblique-winged aviculids were again conspicu- 



