18 PALAEONTOLOGY OF NEW YORK. 



Phacops bombifrons with Phacops cristata, with the more abundant material 

 now accessible, appears to be indisputable. There remains, however, a form of 

 Phacops, abundant in nearly all the outcrops of the Corniferous limestone in 

 the State, which it was not intended to include under the original diagnosis of 

 Phacops bombifrons, and which has hitherto remained unnoticed in any published 

 description, or has been tacitly referred to the species Phacops rana. A careful 

 examination has proven that Phacops rana occurs with extreme rarity, if ever, 

 in this formation, and that the specific affinities of these abundant individuals 

 are much too close to Phacops cristata to justify their recognition as an indepen- 

 dent species. They may be tentatively regarded as a prolific variety of Phacops 

 cristata, under the following designation. 



Phacops cristata, var. pipa, n. var. 



PLATE VIII A, FIGS. 5 [8. 



The essential points of difference between this form and the normal Phacops 

 cristata, are the following: (a) greatly inferior size, (b) absence of the axial row 

 of spines, (c) smaller spines at the genal angles, (d) fewer annulations upon the 

 pygidium, (e) smaller number of corneal lenses, varying, as ascertained from 

 measurements of a large number of specimens, from twenty-three to forty-five 

 for each eye. They agree with Phacops cristata in (a) general proportions, 

 (b) gibbosity of the glabella, (c) presence of the genal spines, which though 

 sometimes faint may always be detected, (d) crenulated sub-marginal sulcus, 

 (e) obtuse termination of the axis of the pygidium, (f) dichotomous annula- 

 tions on the pygidium, (g) similar surface ornamentation. A single pygidium 

 of this variety from the decomposed Corniferous chert of Ontario county, is of 

 exceptional interest as showing on a cast of the inferior surface seven pairs 

 of muscular impressions just within the margins of the axis. 



The dimensions of an average entire individual are; length 26 mm.; width 

 10 mm. The smallest observed has a length of 12 mm., and a width of 7 mm. 



Distribution. Phacops cristata. Oriskany sandstone : Cayuga, Province of Ontario, 

 associated with Dalmanites anchiops, Green, Spirifera arrecta, Hall, Streptorhijnchus 

 (Orthis) hipparionyx, Vanux., Rensselmria ovoides, Hall. Upper Helderberg group : in 

 the Schoharie grit, near Clarksville, Albany county; Schoharie, Schoharie county. 



