1 86 NEW YORK STATE MUSEUM 



from rare (r) to very common (C). The Helderbergian species 

 outnumber the Oriskanian two to one; but this predominant Hel- 

 derbergian aspect disappears when the individual species are exam- 

 ined. The Helderbergian species, Vermipora serpu- 

 loides, Dalmanella subcarinata, Rhipidomella 

 oblata, Nucleospira elegans and Stenochisma 

 f o r m o s a are also found in the calcareous Oriskany of 

 other regions associated with the large normal Oriskany shell s.^ 

 Tentaculites elongatus is much more characteristic of 

 the uppermost calcareous Oriskany than of the lower Helderberg, 

 but it is specially the very typical Oriskany species, B e a c h i a 

 suessana, Meristella lata and Spirifer murchi- 

 s o n i which give the distinct Oriskanian aspect to these beds ; 

 these are abundant and normal in their development, and occur from 

 the base to the top of these beds. Besides these, Rensselaeria 

 subglobosa, Dalmanites dentatus and D . d o 1 - 

 phi, though at present hardly known outside the beds of this 

 region, are more Oriskanian in appearance than Helderbergian. 

 The development of marginal crenulations and spines on the 

 cephalon and pygidium is characteristic of many Devonic trilobites.^ 

 In the genus Dalmanites this is scarcely noticeable in the Helder- 

 bergian but becomes exceedingly conspicuous in the Oriskany, Scho- 

 harie and Onondaga. It is first noticed as slight crenulations on 

 the anterior portion of the cephalic margin of the species p 1 e u - 

 r o p t y X Green of the Lower Helderberg ; in stemmatus 

 Qarke of the calcareous Oriskany this crenulation is extended back 

 along the margin of the cephalon ; while in dentatus Barrett 

 it is greatly accentuated into denticulations. This reaches its maxi- 

 mum development in the regal is Hall of the Schoharie and 

 Onondaga. The appearance of such a highly ornamented Dalman- 

 ites as dentatus Barrett would on a priori grounds be placed 

 above the Helderbergian. All the above named species considered 

 as a whole are so characteristically Oriskanian that it is believed 



Van Ingen & Clark, P. E. N. Y. State Paleontol. An. Rep't. 1902. 

 p. 1203-4; and Clarke N. Y. State Mus. Mem. 3, p. 65-67. 

 -See also Clarke. N. Y. State Mus. Mem. 3, p. 87. 



