REVISION OF PALEOZOIC STELLEROIDEA. 147 



position and arrangement of the ambulacra! pores, can not be 

 clearly made out in the specimen studied. 



"The two oral pieces [proximal adambulacrals] of each of the 

 five pairs are separated by deep sutures, and have an irregular form, 

 being longer than wide, and, like the adambulacral pieces, which 

 they somewhat exceed in size, flattened and depressed at their outer 

 ends, and elevated into crestlike prominences farther in, with a 

 lateral process or thickening on the outer side of each, in which a more 

 or less distinct pit may be seen." Between the pairs of oral adam- 

 bulacral plates are inserted small, single, sub quadrangular plates, 

 the proximal plate of each pair of ambulacral ossicles. Orad to 

 each pair of oral armature plates are situated single hemispheric 

 plates. 



"The surface, and the arrangement of the dorsal parts, are un- 

 known; but they were probably armed with short spines, as some 

 remains of little spines are seen in the matrix at the margin of the 

 disk, at one place. 



"As the extremities of none of the rays can "be clearly seen, the 

 exact breadth of the whole fossil, between the ends of opposite 

 rays, can not be exactly given, but it is evident that the length of 

 one of the rays, measuring from the middle of the disk, must have 

 been a little more than 2 inches, and consequently that the diam- 

 eter across from the extremities of opposite rays could not be less 

 than about 4 inches. The breadth of the disk is 1.20 inches; 

 and that of the rays at their inner ends, 0.70 inch." 



Formation and locality. The single specimen was found in the 

 Maysville formation (Ordovicic), by Mr. U. P. James, on or near 

 Vine Street hill, Cincinnati, Ohio, and is now in the James collection 

 of the Walker Museum of the University of Chicago. 



Remarks. This large species is quite distinct from any other star- 

 fish in having three rows of interbrachial plates, one piece in the proxi- 

 mal, two in the medial, and five or possibly more in the distal row. 

 While the arrangement of these interbrachial plates is different than 

 hi the other species of Petraster, their position is that of this genus. 

 Therefore this species is for the present referred to Petraster. The 

 preservation of this specimen is such that its generic and specific 

 characters will remain hi obscurity until other material is found. 

 It lies with the actinal side buried in the limestone while all of the 

 abactinal plates have been worn away. What one sees is therefore 

 the inner or dorsal aspect of the ventral skeleton. 



PETRASTER SMYTHI McCoy. 



Petraster smythi McCoy, Geol. Surv. Victoria, Prodr. Pal. Victoria, dec. ], 1874, 

 p. 41, pi. 10, figs. 1-16. 



Original description. "Five broad semielliptical lobes meeting 

 at slightly rounded reentering angles, leaving the length and the 



