i3° 



Cincinnati Society of Natural History. 



and with a sharp ridge in the middle ; adambulacral plates a little 

 smaller than the marginal, and with two or three spines to each, taper- 

 ing to a point, and longer than the diameter of the plate; dorsal 

 surface with irregularly-sized and strongly tuberculated or spinous 

 plates ; madreporiform tubercle an oblate spheroid, depressed and 

 marked with fine radiating striae. (Jour. Cin. Soc. Nat. Hist., vol. i, 



P- 3 2 -) 



Locality. — Cincinnati. 



8. — P. dubius Miller and Dyer, 1878. 



Pentagonal; rays longer than diameter of body, tapering to 

 apex; body three-tenth inches in diameter; marginal plates unknown; 

 ambulacral groove deep, angular, formed by two series of plates ; each 

 plate three times as long as wide, and fifteen plates in one-quarter inch 

 on each side of each ray ; adambulacral or oral plates and madrepori- 

 form tubercle unknown. (Contri. to Paleont,, No. 2, p. 5. 



Locality. — Cincinnati, Ohio. 



9. — P. finei Ulrich, 1879. 



• Pentagonal, small; rays 0.3 inch long, rather broad, pointed, 

 expanded about midway between the body and the point ; marginal 

 plates on dorsal surface twelve to fourteen, each with a pit for the 

 articulation of a spine; on ventral surface convex, eleven to twelve, 

 with a piece at junction of rays three times as large as any other, 

 sub-circular and very convex ; ambulacral plates with a sharp ridge, 

 not alternating with adambulacral plates, which are nine to ten in 

 number; dorsal surface of rays with four rows of plates, twelve to 

 fourteen in each row, increasing in size toward the disc, which is com- 

 posed of irregularly shaped and prominent pieces; madreporiform 

 tubercle small, circular, very prominent and marked by strong striae, 

 which become more numerous toward the margin by intercalation of 

 other striae; rays sometimes only four. (Jour. Cin. Soc. Nat. Hist., 

 vol. 2, p. 19.) 



Locality. — Cincinnati, O. 



IO. P. ANTIQUATA (Locke) Sp., 1846. 



Rays five, each about one and one-half inches long; marginal 

 plates rounded ; two rows of adambulacral plates at base of rays and 



