24 PALEONTOLOGY OF NEW YORK. 



Body. 



Length LOO mm. 



\\ idth : > ; J mm. 



The smallest entire specimen .seen is VI mm. lung and 6 mm. wide. Frag- 

 ments of both linger and smaller individuals have been observed. 



lions. Specific Diagnosis. The original of Calymene bufo, Green (Mon- 

 aph of the Trilobites of North America, p. 41), was an imperfect individual 

 redited to an uncertain locality in the State of New Jersey, which may be re- 

 led as of Devonian age. Calymene bufo, var. rana, Green (loc. tit.), 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 tin; 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 ram/, has proved to be an entirely 

 distinct form, Phacops crislntn, var. pipa. (see description of that species, where the 

 differences in the Phacopes of the Hamilton and Upper Helderberg formations 

 are summarized). Phacops rami finds closer allies in the Devonian species of 

 Europe. With Phacops latifrons, Bronn, from the middle Devonian of theEifel 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, he enumerated as follows: Phacops latifrons has (a) the cephalon 

 more compressed laterally; (b) a narrower and more pentagonal glabella; (c) a 

 more coarsely tuhcrcled 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. 



