Cincinnati Society of Natural History. 



length and breadth near middle of ray ; marginal plates moderately 

 convex, twenty-two or twenty-three in number, gradually decreasing 

 in size toward the extremity of ray, each plate marked by a scar for 

 the attachment of a spine ; adambulacral plates somewhat smaller, 

 about the same number, alternating with marginal ones ; basal pair 

 of plates (oral) about ten, elongated triangular, slightly constricted 

 near middle; upper surface of rays with three rows of sub-nodose 

 plates, the outer rows with a strong spine on each plate. (Rept. N. 

 Y. State Mus. Nat. Hist , 1866, p. 284 : 20th Rept. N. Y. State Mus. 

 1870, p. 326.) 



Locality. — Cincinnati, O. 



13. — P. simplex M. and D. 1878. 



Body pentagonal; rays longer than diameter of body and taper- 

 ing ; body four lines in diameter, and rays probably two inches in 

 length when perfect ; marginal plates nine or more, the one at the junc- 

 tion of any two rays large and angular-ovate, the smaller end extend- 

 ing up between two marginal plates, while the larger one extends into 

 an angle formed by two adambulacral plates ; ambulacral groove very 

 narrow ; adambulacral plates about twenty-two, somewhat oblong, 

 their breadth extending along the length and their length across the 

 ray; oral plates ten, irregular or elliptical, with a triangular extension 

 into the oral opening. (Jour. Cin. Soc. Nat. Hist., vol. 1, p. 29.) 



Locality. — Raysville, O. 



14. — P. longibrachiatus S. A. Miller, 1878. 



Pentagonal ; rays more than twice as long as diameter of body ; 

 breadth of body about six lines, length of rays about one and three- 

 tenth inches; marginal plates spheroidal, gradually enlarging from tip 

 to base of ray, about thirty-four, or a few more, in number, junction 

 between rays formed by two pieces ; ambulacral groove very narrow ; 

 ambulacral plates of the same form as, but larger than, marginal plates 

 near ends of rays, but smaller than them near the body; no ambulac- 

 ral plates within four plates of the two pieces at junction of rays. 

 (Jour. Cin. Soc. Nat. Hist., vol. 1, p. 102.) 



Locality. — Clarksville, Ohio. 



