EARLY DEVONIC HISTORY OF XEW YORK AND EASTERN NORTH AMERICA 



123 



ribs 10 or 11 in number, the last three of which are simple and faint but all 

 the rest very strongly duplicate throughout their entire extent, becoming 

 obsolete at or just within the margin. The axis is broad and the dorsal 

 furrows rapidly approximate ; it bears 11 or 12 segments and its apex is not 

 abrupt but merges into a low median ridge continued to the end of the tail. 

 The terminal spine is little more than a broad and short rather obtuse 

 expansion. The surface of the test is finely granulate except for a few scat- 

 tered coarser pustules on the axis. The specimens average 26 mm in length 

 and 29 mm in width. 



This style of pygidial structure with strongly bifurcate pleural ribs is 

 freely represented in the faunas of the early Devonic elsewhere by such spe- 

 cies as D. b i s i g n a t u s Clarke and D. d e n t a t u s Barrett (Oriskany), 

 D. V c i t i and D. p h a c o p t y x. D a 1 m a n i t e s d e n t a t u s, its associate 

 D. d o 1 p h i Clarke and D. v e i t i are known to have a crenulated or 

 dentate border but D. phacoptyx is without this feature. 



Localities. Grande Greve and Indian Cove. 



Species name. A. P. Low, Director of the Geological Survey of Canada 

 and early worker in Gaspe geology. 



Dalmanites phacoptyx Hall & Clarke 



Plate 7, figures 5-10 



Dalmanites phacoptyx Hall & Clarice. 



7:31, pi. 9, fig. 23-27 

 Dalmanites p h a c o p t y x Clarke 



pi. 2, fig. 10 



Palaeontology of New York 

 Mem. 3. N. Y. State Museum. 



1900. p. 19, 



This species was based upon a 

 series of large, coarsely tubercled and 

 echinate but incomplete pygidia, hav- 

 ing a slender but extended tail spine. 

 The original specimen was from the 

 so-called Onondaga limestone at 

 North Cayuga, Ontario, an horizon 

 which is now recognized as included 

 in the beds termed by Schuchert the 

 Decewville formation and whose 

 fauna is a commixture of Oriskany 

 and Onondaga species. 



Among the commoner speci- 

 mens in the Grande Greve limestone 

 are pygidia of this type. These are 

 broadly triangular plates of nearly 

 equal length on the three sides, gently and regularly convex with relatively 

 narrow and slender axis. The pleural ribs are grooved but this duplication 



D,-ilmaiiites phacoptyx. A portion of the cranidium 

 and cheek spine, showing the spinules on both. 

 From tlie slab represented on the adjoining plate 



