CRUSTACEA. 
17 
Observations. Specific Diagnosis. The diagnostic characters of this species 
are very clearly defined, and may be summarized as follows: (a) the axial 
row of spines extending as far as the pygidium, (b) the short, stout spines 
on the genal angles, (c) the strongly protuberant glabella, (d) the com¬ 
parative absence of tuberculations, except on the glabellar surface, (e) the ten 
or eleven crenulations upon each side of the sub-marginal furrow of the 
cephalon, (f) the dichotomous annulations of the pygidium. In the summary 
of these features Phacops cristata differs from any species known outside of the 
State of New York, and therefore cannot be satisfactorily compared with any 
extra-limital forms in the United States. Phacops fecundus, Barrande, from 
the F, G and H etages of Bohemia, and the lower and middle Devonian 
of the Eifel, Westphalia and the Hartz, presents a striking similarity in 
outline, in the protuberant glabella and the grooved pygidial annulations. 
Phacops Logani, Hall, from the Lower Helderberg group, bears a pygidium with 
similarly bifurcate ribs and obtusely terminated axis, and a cephalon with minute 
spines on its genal angles, but it is distinguished from Ph. cristata by the con¬ 
spicuous nodes along the margins of the axis of the thorax, the stronger tuber- 
culation of the surface, and the absence of an axial row of spinules. Phacops 
Trajanus, Billings, also from the Lower Helderberg group, bears bifurcate annu¬ 
lations on the pygidium, but as this species is incompletely known, its further 
resemblances to Ph. cristata cannot be indicated. As described and limited in 
the original description {loc. cit.) Phacops cristata was made to include all the 
forms of this genus occurring in considerable abundance in the Schoharie grit, 
and these exclusively, with the exception of a single specimen from the Upper 
Helderberg limestone at the Indian quarries, Onondaga county. The species 
Phacops bombifrons was erected at the same time for certain cephalic shields and 
pygidia from the Upper Helderberg limestones, in which a degree of similarity 
to Phacops cristata was acknowledged, but in which a more prominent and pro¬ 
tuberant glabella, wider occipital furrow, narrower palpebral sulcus and stronger 
palpebral lobe, were regarded as distinguishing characters. With due allowance 
made for differences in the mode of preservation in the sandstone and lime¬ 
stone of the Upper Helderberg, the specific identity of forms referred to 
