Manual of the Paleontology of the Cincinnati Group. 



133 



C. Ambulacral grooves unknown. 

 15. — P. incomptus Meek, 1872. 



Pentagonal, small; rays short, about 0.35 inch long and one and 

 one-half times as long as broad, tapering rapidly to the apex and 

 obtusely angular in form; body about equal to rays in diameter; 

 dorsal surface of rays with three or perhaps four rows of plates, wider 

 than long, about nine in each row, increasing rapidly in size toward 

 the base : disc composed of smaller pieces ; all the plates granulose 

 but apparently spineless; madreporiform tubercle rather small, oval or 

 circular, nearly flat and marked by fine irregularly interrupted striae. 

 (Am. Jour. Sci , 3d ser. vol. 3, p. 275 : Ohio Paleont., vol. 1. p. 64.) 



Locality.— Cincinnati, O. 



16. — P. clarkanus S. A. Miller, 1880. 



Pentagonal ; rays one-half the diameter of the body ; rapidly 

 tapering to a point and one-fifteenth of an inch long; body two- 

 fifteenths inch in diameter; marginal plates probably six on each side 

 of each ray, with three series of interlocking plates on the dorsal 

 surface of each ray between the marginal plates; madreporiform 

 tubercle and ventral surface unknown. (Single specimen.) (Jour. 

 Cin. Soc. Nat. Hist. vol. 1, p. 102. as P. clarkei Ibid., vol. 3, 1880, 

 p. 236 as P. clarkanus .) 



Locality. — Cincinnati, O. 



Remarks. — The original name proposed for this species was 

 Clarkei. It was subsequently found that this name was preoccupied 

 and so the name clarkanus was substituted. 



17. — P. ANTIQUA (TrOOSt) Sp., 1 835. 



Body of medium size; rays five, flexuose ; marginal plates large, 

 somewhat quadrangular, the outer faces subnodose ; basal plates of 

 the series single, broadly triangular, with slightly truncated lateral 

 angles, the obtuse angle directed toward the axil of the ray ; the small 

 triangular space between the marginal and adambulacral plates filled 

 by small granules or plates; adambulacral plates small, twice as 

 numerous as the marginal ones; basal plates of the range elongated, 

 triangular ; ambulacral grooves with a single row of subquadrate 

 ossicles alternating with the adambulacral plates ; dorsal surface 



