THE DEVONIAN PERIOD. 459 



less impressive as a factor of the fauna. The brachiopods of the Oris- 

 kany were largely of the same genera as those of the Helderberg, but 

 the species were new. Some of the genera, as Eatonia and Rensselceria, 

 were confined to these two faunas; others had a wider range. Of the 

 latter, many were represented later in the Onondaga, and some in the 

 Hamilton faunas. 



It is important to note that in South America there were several 

 species which bore a strong Oriskany facies, and in some cases there 

 was complete specific identity, as in the notable form Anoplotheca 

 flabellites. 



Mollusks abundant and large. — While the mollusks were much 

 less amply represented than the molluscoids, they showed some striking 

 characters which help to further characterize the fauna. The gas- 

 tropods were the most abundant of the mollusks, and the capulicls 

 were their leading form, as in the Helderberg epoch. Not less than 

 60% of all the known Oriskany gastropods were capulids. Some of 

 them were exceptionally large and plump, reaching lengths of four 

 inches, and mouth-expansions of two and a half inches. The Helder- 

 berg capulids had been without spines, but the spine-bearing species 

 Platyceras nodosus appeared in the Oriskany fauna, although it became 

 more conspicuous in the later Onondagan. 



The pelecypods were not very abundant, but, like the brachiopods 

 and gastropods, they were phenomenally large and coarse, some of them 

 being five inches across. These unusual sizes, affecting three dis- 

 tinct types, imply that the cause lay in conditions congenial to the 

 types and not in the types themselves, except as they were well con- 

 stituted to respond to the conditions. The pteropods were repre- 

 sented by the Conularia — and even that was large — and by large ten- 

 taculites; while the former powerful cephalopods were reduced to a 

 single species, so far as the known record shows. 



Scantiness of trilobites, corals, crinoids, and fish. — The trilobites 

 were not abundant and were chiefly species that had a larger develop- 

 ment in the Onondaga. They were perhaps even Onondagan forms 

 that became mingled with the late Oriskany forms after the two faunas 

 came in contact, as explained later. In the calcareous phase of the 

 Oriskany, however, there were several trilobites more or less closely 

 allied to Helderberg forms. Corals, crinoids, and cystoids were rare, 

 as might be expected from the nature of the formation; so also were 



