132 PALEONTOLOGY OF NEW YORK. 



Axis very prominent, semi-cylindrical. 



Pleura' flat for about one-half their width, thence sloping gently to the 



Pygididm very elongate-triangular, the length being equal to the width. 



The axis tapers to an obtuse termination considerably within the scarcely 

 thickened border; composed of twenty-two annulations, which are vertical 

 on the sides, but have a gentle anterior curve toward their summit. 



Pleura flat near the axis, thence curving somewhat abruptly outward and 

 downward ; bearing twelve annulations, which terminate in a broad, sloping 

 1> order abruptly recurved at the edge. 



Surface finely granulose. 



Observations. There exists a great deal of doubt both as to the generic status 

 and the geological age of this species. The original and type specimen was 

 presented many years ago by the Rev. Mr. Nash, of Des Moines, Iowa, together 

 with specimens of Phacops rana, and was said to have been found in association 

 with the latter at some point to the north-east of that place. This was the 

 only specimen of the species known until certain others were described by 

 Mr. H. S. Williams (loc. cit.) from a blue limestone near Madison, Greenwood 

 county, Kansas, and he has suggested that these may have been derived from 

 rocks not older than the Carboniferous. Mr. Williams' specimens were obtained 

 from Mr. Edwin Walters, of Hickman, formerly of Madison, Kansas, who, in 

 response to inquiries, writes that he has found this species in association with 

 Phacops bufo {rana). Admitting its association with this well-known and 

 characteristic fossil, its geological age would appear to be that of the Hamilton 

 group. 



On the other hand the species, in many important structural features, is 

 more closely related to the Carboniferous Phillipsicc than to typical forms of 

 Proetus. The possession of but nine thoracic segments, which appears to be a 

 normal feature of the species at maturity, is known in but one other species of 

 Proitus, viz., P. sculpius, Barrande, from the etage G. For the genus Phillipsia 

 this is the normal number. Moreover, the oval, slightly constricted glabella, 



