l66 NEW YORK STATE MUSEUM 



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 thoracic segments knotted at the dorsal furrows 

 as in large specimens of Ph. 1 o g a n i. 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. 1 o g a n i. 



The variations of expression in the representatives of the genus 

 Phacops in the New York Devonic are slender and identifications 

 are always obscure. Fixing upon the following characters as 

 critical, viz, the .cristation of the genal angles, the knotting of the 

 thoracic segments and the grooving of the pleural ribs on the 

 pygidium, we may tabulate the species thus : 



Cheeks Thorax Pygidial ribs 



P. logani (Helderbergian) faintly spined knotted duplicate 



P. cristatus (Schoharie grit) strongly spined smooth duplicate 



P. c ristat a var. pip a (Onondaga) faintly spined smooth duplicate 



P. bombifrons (Onondaga) smooth smooth duplicate 



P. r a n a (Hamilton-Ithaca) smooth smooth simple 



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

 P. logani; the Perce form, which is always small, is a near ap- 

 proach to the typical expression of the species. 



Lower Devonic. Everywhere along the Florillon from Ship- 

 head to Little Gaspe, and in the blocks of limestone from the sec- 

 ond range found in the stream bed at Peninsula. Also at the 

 Ruisseau du Grande Cavee associated with Dalmanites grif- 

 fon i, and in Perce rock, P. Q. 



Phacops (Phacopidella) nylanderi nov. 



This is an addition to the peculiar group of early Devonic species 

 of which we recognize the following other members : P. b r a s i 1 - 

 i e n s i s (Maecuru) , P. a n c e p s (Decewville) , P. correlator, 



Phacops (Phacopidella) nylanderi 



New York Oriskany and Gaspe sandstone. We have noted in what 

 respects this group, departs from the structure presented by P. 

 d o w n i n g i a e, the exemplar of the generic group Acaste=Pha- 



