CONTRIBUTIONS TO PALAEONTOLOGY. 95 



PHACOPS CRISTATA(n.s.). 

 Entire body elongate; length a little more than twice the breadth. 

 Head nearly semicircular; width a little more than twice the 

 length. Thorax about one-seventh longer than wide. Pygidium 

 semielliptical, about two-thirds as long as wide. Glabella promi- 

 nent, ventricose, the longitudinal furrow separating the eye very 

 narrow; neck small; occipital ring furnished with a small pro- 

 minent spine. Eye prominent, narrow above, having six or seven 

 lenses in the central vertical row^s, and thirteen or fourteen rows 

 from the anterior to the posterior side : the anterior angle has a 

 single lens. Axis of the thorax prominent, angular, semielliptical, 

 and marked by eight or more rounded rings, the summit of each 

 ring having a short vertical spine. Lateral lobes flat for half their 

 width and bent abruptly downwards, marked by six or seven ribs. 

 Surface granulose; the glabella papillose or tuberculous. 



This species is readily distinguished by the crest of spines upon the back, 

 and, in the separated heads, by the spine upon the occipital ring, which is 

 very conspicuous even in the casts. The eyes are proportionally narrower 

 and higher than in P. bufoj var. rana; the number of lenses in the vertical 

 rows being more, while in the lateral direction there are fewer rows. 



There is evidence of still another species in the same geological associa- 

 tion, which may be indicated by the anterior extension of the frontal lobe 

 of the glabella. 



Geological formation and locality. In the Schoharie grit : Helderberg 

 mountains and Schoharie. 



The most satisfactory specimen for examination, which I have seen, is a 

 mould in the gritstone which preserves the impressions of all the parts : 

 this specimen is in the Cabinet of the Albany Institute. Besides well-marked 

 fragments of the head, I have an entire specimen from which the crust is 

 removed, received many years since as coming from the Schoharie grit, and 

 the condition of the specimen corroborates that opinion ; but, unfortunately, 

 the distinguishing specific features are mainly obliterated. 



PHACOPS BOMBIFRONS (n.s.). 

 In the limestone of the Helderberg mountains, there is a Phacops which 

 cannot be identified with any of the varieties of P. hufo^ or P. hufo, var. 

 rana. The specimens which I have seen are separated heads, with a very 

 prominent glabella, a neck wider than in the P. cristaia^ a narrow furrow 

 between the eye and the glabella ; the eye elevated and narrower than in 

 P. ranUf with the palpebral lobe more prominent. The limitation of the 



