Mi! T/u. Aimi'iciiii Geologist. Feb. 1891 
that in Progtu8, bul with the extremities of the abruptly reflected 
annulations produced into shorl spines. In this genus, of which 
much is to be learned, are included five species from Bohemia, 
the Rhine and the Hartz. 
Cyphaspis appears in one species ( C. hydrocephala ELoemer), a 
near ally of G. minusdula Hall, of the Corniferous limestone. 
The reappearance- of the genus Arethusina from the middle 
Silurian is a feature of interest. 
The species of Phacops all have the peculiarities of the early 
representatives of the genus, well defined, linear glabellar furrows, 
and grooved pygidial pleurae, being in contrast to the later repre- 
sentatives in which both characters are obsolescent. The species 
of the Lower Helderberg, Oriskany, Schoharie grit and Cornifer- 
ous limestone are all provided with these features, while P. logani 
the abundant species of the Lower Helderberg, alone has the 
lobation of the lateral margins of the axis which characterizes 
/'. breviceps of etage /,. The form described as Phacops cf. 
Zorgensio Kayser lias the subpentagonal glabella characterizing 
an undescribed species in the Oriskany of New York. 
Lichas haueri is closely allied to L. ptyonurus Hall from the 
Coralline limestone (Niagara) of Schoharie, X. Y.. and L. 
( .l/vy/.v ) maureri is represented in the Corniferous by Arges contu- 
sus Hall. In Acidaspis vesiculosa Beyrich we have a type of 
structure which Mas designated by Corda, as Trapelocera and by 
Warder as Ceratocephala. The group has but a single known 
representative in American faunas. .1. <hni<ii Hall, of the Niagara 
group, a synonym of Ceratocephala goniata, Warder. Acidaspis 
pigra Barrande, differs from .1. callicera Hall of the Upper Hel- 
derberg in minor respects only. 
Crotalocephalus (cordai) is represented in the Niagara fauna 
by C niagarensis Hall, but with this species the existence of the 
Cheirurus-tyj)e ended, as far as known, in our Paheozoie. The 
abundance of Bronteus with spinous pygidial margins, is a feature 
emphasizing the Devonian value of the faunas. This type of 
structure (Thysanopeltis Corda) attains a maximum development 
in the later Devonian, and with us. is represented in the B. tul- 
lius Hall, of the Tullv limestone, while it does not appear in any 
of the earlier faunas. The Niagara species and the Lower Helder- 
berg. />. barrandii Hall, have smooth-margined pygidia and of 
