240 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



lacral, adambulacral and marginal series, which are united by their 

 edges, and apparently not imbricating, the projecting ot oblique 

 anterior face of the marginal plates bearing spines which are inclined 

 toward the extremity of the ray. Margins of the rays alated by the 

 extension of the disk. 



''I had originally united this form Avith Eugaster, but further ex- 

 amination has shown the ray to have a range of marginal plates 

 outside of the adambulacral plates, and I am unable to discover any 

 such feature in Eugaster logani. 



"This and the preceding genus [Eugasterella] belong to the Ophiu- 

 ridse, to which may also be referred the genus ProtasterJ' 



" Note. — It is only as these pages are going to press that my atten- 

 tion has been directed to the similarity of structure in the ray of 

 Palseocoma of Salter with that of the proposed genus Ptilonaster. 

 In this illustrated species of the former genus {Palseocoma marstoni) 

 the disk is proportionately larger, and the rays much shorter, while 

 the outer range of plates is represented as imbricating; but being 

 characterized by a double row of plates bordermg the ambulacral 

 area, it must be regarded as very nearly related if not generically 

 identical with Ptilonaster.^' 



Gregory comments on Ptilonaster as follows: "Tliis genus is an ally 

 of Eugaster; * * * it is, however, generically distinct. I only 

 know it from HaU's figures, and therefore prefer to leave the prep- 

 aration of a formal diagnosis to an American palaeontologist." 



Genoholotype and only species. — P. princeps HaU. 



PTILONASTER PRINCEPS Hall. 



Ptilonaster princcps Hall, Twentieth Rep. N. Y. State Cab. Nat. Hist., 1868, 



p. 292; rev. ed., 1868=1870, p. 334, pi. 9, fig. 9. 

 Palxocoma princeps Miller, N. Amer. Geol. Pal., 1889, p. 267. 



Original description. — "The specimen consists of the impression of 

 the greater part of one ray, mth parts of two others, and intervening 

 portions of the disk. The disk has extended along the ray nearly an 

 inch from the center 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 4^ inches in length; its greatest width 

 is outside of the disk, 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 center; of these at 

 least seven ranges have been included within the disk. The ambula- 

 cral 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 toward the extremity of the ray. Near 

 the base of the ray there are 12 plates in the length of an inch. 



