24 PALEONTOLOGY OF NEW YORK. 
Body. Cephalon. Thorax. Pygidium. 
Length_ 100 mm. 32 mm. 38 mm. 30 mm. 
Width_ 53 mm. 53 mm. 51 mm. 47 mm. 
The smallest entire specimen seen is 12 mm. long and 6 mm. wide. Frag¬ 
ments of both larger and smaller individuals have been observed. 
Observations. Specific Diagnosis. The original of Calymene bufo, Green (Mon¬ 
ograph of the Trilohites of North America, p. 41), was an imperfect individual 
accredited to an uncertain locality in the State of New Jersey, which may be re¬ 
garded as of Devonian age. Calymene bvfo, var. rana, Green (loc. cit.), is cited 
by the same author as occurring at Seneca, Ontario county, N. Y., which is a 
locality on the shales of the Hamilton group, and as this Phacops is the only 
representative of the genus known to occur in this formation in the State of 
New York, no doubt can remain of the correctness of the specific reference. 
Phacops rana is very generally disseminated throughout the different horizons 
of the Hamilton group, from the Marcellus shales to the top of the Tully 
limestone. It may also occur in extremely rare instances in the Upper 
Helderberg limestones, but the species of Phacops so abundant in the latter 
formation and usually referred to Phacops rana, has proved to be an entirely 
distinct form, Phacops crUtata, var. pipa. (see description of that species, where the 
differences in the Phacopes of the Hamilton and Upper Helderberg formations 
are summarized). Phacops rana finds closer allies in the Devonian species of 
Europe. With Phacops latifrons, Broun, from the middle Devonian of the Eifel and 
elsewhere, it is closely similar in general proportions and most of its superficial 
details, both species having the pleural annulations of the pygidium simple and the 
termination of the axis acute (a noteworthy agreement). Points of difference 
may, however, be enumerated as follows; Phacops latifrons has (a) the cephalon 
more compressed laterally; (b) a narrower and more pentagonal glabella; (c) a 
more coarsely tubercled glabella and smoother cheeks; (d) more numerous 
corneal lenses, varying between seventy-seven and ninety for average adult 
individuals; a variety of this species having as many as one hundred and 
twenty. 
