88 NEW YOEK STATE MUSEUM 



the Onondaga. In Cryphaeus of the Mesodevonic the lobation 

 is retained, but the marginal ornament has disappeared from the cepha- 

 lon and appears on the pygidium. The cephalic ornamentation in the 

 species, D. stemmatus, Oriskany, D. regalis, and D. anchiops 

 Schoharie grit, and D. selenurus, etc. of the Onondaga limestone is 

 associated with lobal coalescence and may be looked on as an instance 

 of morphic equivalence. 



Phacops is represented by P. 1 o g a n i (P. hudsonicus). 

 The species mentioned are typical Phacopes, forms in which the 

 glabellar lobes are almost or quite coalesced, the glabella ventricose and 

 the pygidium short. Such typical forms are not known in any 

 earlier American fauna. In general this genus divides itself 

 into two groups, in one of which the glabellar furrows are 

 represented by faint, linear impressions, and the pleura of the pygidium 

 are duplicate ; in the other the furrovvs are obsolete and the pygidial 

 pleura simple. The latter is believed to be limited to Mesodevonic 

 faunas (P. r a n a , Hamilton, P. latifrons, Eifelian), while the former 

 is widely disseminated as a characteristic Paleodevonic group. To 

 this belong the Helderbergian species. 



Of Acidaspis we have two species ; A. t u b e r c u 1 a t a is re- 

 lated to the Onondaga A. callicera. The remarkable A. h a m a t a 

 (genus Dicranurus) with long, recurved cervical horns, finds its only 

 known analogue and almost specific identity in the A. monstrosa, 

 Barrande, of the etage G (Paleodevonic). 



L i c h a s is represented by L. pustulosus, the most abundant 

 species, which seems to indicate a type of subgeneric structure not 

 elsewhere presented. L. consanguineus belongs to the subgenus 

 A r g e s and has species both in the Siluric and Devonic. 



The single species of Proetus (P. protuberans) in the 

 Helderbergian of New York is of rare occurrence. In type of struc- 

 ture it conforms throughout to the series P. conradi, Oriskany, P. 

 angustifrons, Schoharie grit, P. c 1 a r u s , Onondaga limestone and 

 P. r o w i of the Hamilton group. 



Cordania makes its earliest appearance in the Helderbergian, 



