292 TWENTIETH EEPORT ON THE STATE CABINET. 



Ptilonaster princeps (n. s.). 



PLATE IX. FIG. 9. 



The specimen consists of tlie impression of the greater part of one ray, 

 with parts of two others, and intervening portions of the disc. 



The disc has extended along the ray nearly an inch from the centre of the 

 body; the plates are small, and have been furnished with slender spinules, 

 The ray is strong and extremely elongate, having been at least four and a 

 half inches in length : its greatest width is outside of the disc, where it 

 measures seven-sixteenths of an inch. The ventral side of the ray shows 

 three series of plates; ambulacral, adambulacral and marginal, on each 

 side of the centre ; of these at least seven ranges have been included within 

 the disc. The ambulacral plates are a little wider than long, arranged in 

 alternating order. 



The pores penetrate the interstices near the outer extremity of the plates, 

 while the partial or obsolete pores are obscure, becoming deeper and more 

 conspicuous towards the extremity of the ray. Near the base of the ray 

 there are twelve plates in the length of an inch, and fourteen plates in the 

 same distance in the central portion, and towards the extremities there are 

 twenty or more in the same space. 



The marginal plates are subhexagonal, a little longer than wide, and 

 ornamented by long slender spines on their outer margins. 



This is a much larger and more robust species than the Eugaster logani, 

 and in its entire condition it is the largest starfish known in our palaeozoic 

 rocks. 



Geological formation and locality. In the Chemung group. The specimen 

 IS in a brownish-gray sandstone, which weathers to a very light ashen color. 

 It was received from Henry S. Randall, Esq. of Cortlandville, in the 

 vicinity of which place it was obtained. 



Note. — It is only as these pages are going to press that my attention has 

 bfon directed to the similarity of structure in the ray of Pal^coma of 

 Halter, and that of the proposed Genus Ptilonaster. In the illustrated 

 species of the former genus {Palceocoma marstoni) the disc is proportionally 

 larger, and the rays much shorter, while the outer range of plates is repre- 

 sented as imbricating ; but being characterized by a double row of plates 

 bordering the ambulacral area, it must be regarded as very nearly related, 

 if not generically identical with Ptilonaster, 

 12 



