Ilelderberg Limestones in North America. Ill 
occipital ring to anterior border, with furrows and lobes faint or 
obsolete, rounded genal angles and relatively broad rhachis on 
the pygidium ; a type not common in America. l>ut represented 
in the Lower Ilelderberg by its only species, P. protuberans Hall 
and in the Corniferous limestone by P. folliceps Hall. A second, 
less abundant type is that of P. eremita Barrande ( etage/1), charac- 
terized by the shorter, more subquadrate, depressed and furrowed 
glabella, and especially by the short pygidium with narrow, acute 
rhachis and obscure pleural annnlations ; with this maybe com- 
pared the P. cori/coens Conrad, of the Niagara group, probaby 
the only representative of this phase of structure known in our 
faunas. A third is that of P. holzapfeli Novak, ( .Eon in Burmeis- 
ter ) with violin-shaped glabella and spinous genal angles, as in 
P. canaliculatus Hall of the Corniferous limestone, a fourth. 
P. waldschmidti Novak, which seems in most respects to exemplify 
the type of structure represented most abundantly in our Palaeo- 
zoic faunas, as shown in P. augustifrons Hall of the Schoharie grit. 
P. clarus Hall, of the Corniferous, P. rowi G-reen, P. prouti Shu- 
mad, P. phocion Billings, P. nevadce Hall, of the later Devonian. 
A fifth type of structure is P. filicostatus Novak, which is re 
markable for its broad, flabellate pygidium and rapidly tapering 
glabella, characters which the author has considered of such dis- 
tinctive importance that he has proposed to designate the group 
which it represents by the new term Tropidocoryphe-Prionopeltis 
Corda, in part. With these forms may be compared the P. plani- 
marginatw Meek, of the Corniferous limestone. Another and 
sixtli type of proetid structure is represented by P. planicauda 
Barrande, a form with fimbriated pygidium, hut differing from 
P. archiaci Barrande. and other species belonging to the subgenus 
J i /nrt<>ni(lrs Barrande, in the shorter rhachis and fewer annula 
tions of the pygidium. For this group, represented by the form 
mentioned and P. dentatulus Novak, the subgeneric term Phce 
tonellus is proposed. It is probable that the Phceton denticulatus 
Meek, from the Devonian of Nevada, is a member of the same 
group, while it is a matter of doubt whether typical forms of 
Barrande's Phceton Phcetonides (not Phcetonides A.ngelin > have 
heen found in our palaeozoic faunas. The author establishes an 
other new generic group, Cyphaspides, which is based upon apecu 
liarly subquadrate pygidium having in general the structure of 
