REVISION OF PALEOZOIC STELLEROIDEA. 121 



however, can be seen in places, on each side of the ambulacral 

 furrows, and alternating with a row of similar but slightly smaller 

 adambulacral pieces, the number of pieces in each side of these being 

 about the same. [In the proximal portion of a ray there are 19 

 marginal plates in 40 mm.]. The marginal pieces seem each to 

 connect with the adjacent range of dorsal pieces, at places in the 

 rays, by a little central salient point only, while those of both series 

 are roughened by numerous comparatively coarse granules [all of 

 which bear small spines], and each piece (especially [only] of the 

 marginal row) also shows a small central pit for the articulation of 

 a spine. These spines are larger than those connected with the 

 dorsal pieces, being generally about 0.22 inch in length and 0.05 inch 

 in thickness; they are smooth, straight, rounded, slightly thickened at 

 the attached end, and tapering at the free end to a slightly blunted 

 point. [The adambulacral plates also possess these large spines, 

 which are inserted on the distal inner edge of each plate.]" 



In each interbrachial area there are two pairs of wedge-shaped 

 pieces and a single diamond-shaped interbrachial marginal plate. 

 There are at least 4 (and may be as many as 10) pairs of adam- 

 bulacral plates orally or in the actinal interbrachial areas, the terminal 

 pair being of the oral armature. 



Ambulacral plates much wider than long, increasing rapidly in 

 width toward the mouth. Each plate is carinated as in P. sped- 

 osus and proximally as in P. magnificus, with the podial openings 

 confined to the extreme outer edge of the ambulacral furrows. 



Formation and locality. Found at Cincinnati, Ohio, in the Mays- 

 ville beds, about 200 feet below the top of the hills. The ,holo type 

 is in the Dyer collection of the Museum of Comparative Zoology, 

 Harvard University (No. 13). Another specimen from near the top 

 of the Maysville at Cincinnati, preserving only the disk and showing 

 best the actinal area, is in the Gurley collection of the University 

 of Chicago (No. 10989). Originally this individual appears to have 

 been larger than the holotype. 



Remarks. The relationship of this species is with P. spinulosus, 

 but the larger size, greater development of both dorsal and ventral 

 spines, absence of columnar arrangement of the abactinal plates, 

 and the presence of five instead of two or three interbrachial marginal 

 plates will readily separate P. dyeri from the latter species. Even 

 though this form appears to have attained a larger growth than 

 P. magnificus, which it resembles in some characters, it differs in 

 being more ponderous in its skeleton and in the far stouter and 

 longer actinal spines. 



Regarding the generic position of Palseaster dyeri, Meek wrote: 



" Possibly I should have called it Petraster dyeri, for if the apparent 

 presence of a few disk plates on the ventral side between the mar- 



