EARLY DEVOXIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA II9 



Phacops logani Hall van gaspensis nov. 



Plate 10, figures 5, 6, 10-16 



The species of Phacops very common in the Grande Greve limestones 

 presents itself in all variations of size. The larger forms are coarsely 

 tubercled on the glabella and in these there is a well defined row of knobs 

 on the thoracic axis along the dorsal furrows, shown always to best advan- 

 tage on the internal cast. The pygidium has 4-5 duplicate lateral ribs. 

 Added to these critical features is the absence of genal spinules. The 

 larger of these forms have a close and distinct resemblance to the species 

 described by Hall as Ph. bombifrons' from "the limestone of the 

 Helderberg mountains," by which was intended that now known as the 

 Onondaga limestone, a resemblance expressed in all the characters of 

 the cephalon which carries a full bombate glabella. VVe have no means of 

 knowing the other parts of the animals thus designated by Hall. In the 

 Grande Greve rocks these large, coarsely tubercled cephala have the tho- 

 racic segments knotted at the dorsal furrows as in large specimens of 

 P. logani. In smaller specimens these thoracic characters are obscured 

 except in the cast, but the cephalic shields of the latter do not show the 

 spinules of the Perce species and of typical P. logani. 



The variations of expression in the representatives of the genus Phacops 

 in the New York Devonic are slender and identifications are always obscure. 

 P"ixing upon the following characters as critical, viz., the cristation of the 

 genal angles, the knotting of the thoracic segments along the dorsal furrows 

 and the grooving of the pleural ribs on the pygidium, we may tabulate the 

 species thus : 



Cheeks 



P. logani (Helderbergian) faintly spined 



P. cristatus (Schoharie grit) strongly spined 



P. cristatus var. p i p a (Onondaga) faintly spined 



P. b o ni b i f r o n s (Onondaga) smooth 



P. ran a (Hamilton-Ithaca) smooth 



In this schedule the Grande Greve species takes a place close to 

 P. logani; the Perce form, which is always small, is a nearer approach to 

 the typical expression of the species. 



Localities. Everywhere along the Forillon from Shiphead to Little 

 Gaspe, and in the blocks of limestone from the second range found in the 

 stream bed at Peninsula. Also at the Ruisseau du Grande Cavee associated 

 with Dalnianites griffoni. 



Thorax 



Pygidial ribs 



knotted 



duplicate 



smooth 



duplicate 



smooth 



duplicate 



smooth 



duplicate 



smooth 



simple 



'Descriptions of New Species of Fossils. 1861. p. 67; N. Y. State Cab. Nat. Hist. 

 15th An. Rep't. 1862. p. 95; Illustrations of Devonian Fossils. 1876. pi. 6, fig. 22-24, 29. 



