324 



NORTH AMERICAN INDEX FOSSILS. 



174. P. callicephalus (Hall). (Fig. 1639, c,g^.) Ordovicic. 



Pygidium shorter and less triangular than in P. intermedius, and 

 with its axis not constricted in the middle nor extending to the 

 posterior end. 



Lowville-Trenton of New York, New Jersey, Kentucky, Minne- 

 sota, Winnipeg, etc. 



Fig. 1639. a, b, Pterygo7netopns inte7'medius , erwoWed and pygidium; r, d, P. 

 callicephalus^ cephalon and pygidium ; e, P. ebo7'aceus, cephalon. (After Clarke. ) 



175. P. intermedius (Walcott). (Fig. 1639, a, Z?.) Ordovicic. 



Pygidium triangular, its axis constricted in the middle. 

 Trenton of New Jersey, Illinois, Wisconsin and Minnesota. 



176 P. eboraceus Clarke. (Fig. 1639, ^.) Ordovicic. 



Differs from P. intermedius in its broader occipital ring which 

 bears at the center a conspicuous tubercle. 



Trenton of New York and Frobisher Bay. 



LIX. Dalmanites Emmrich. 



Glabella widest anteriorly but not much expanded, marked with 

 two or three distinct lateral furrows. Genal angles produced into 

 spines. Eyes large, prominent, with many distinct lenses. For 

 facial sutures see Fig. 1640. Thorax of 11 segments with grooved 

 pleura. Pygidium large, triangular, frequently with terminal 

 spines and 11 to 20 or more annulations. Ordovicic-Devonic. 



The subgenus Synphoria Clarke includes those forms which have 

 the first and second lateral glabellar lobes more of less coalesced. 



Corycephalus Hall includes those forms with the frontal and 

 lateral margins of the cephalon bearing a single row of short 

 spines. 



