HEXACEINID^. 799 



winch in tliis species do not penetrate the test, but rest exclusively against 

 the sloping faces of adjoining plates. The anal side has two interambulacral 

 pieces in the first row, and three in the second, which latter are followed by 

 numerous smaller plates. Anal opening subcentral, directed obliquely up- 

 wards. The posterior oral occupies a central position, being pushed in 

 between the other four; the latter rest against the interambulacral j^lates. 

 ,The form of the appendages is not definitely known, but we judge from the 

 form of the sockets, which are narrow and elongate, and from fragments in 

 contact with the specimen, that they were probably similar in form to those 

 figured by Lyon (Geol. Eep. Kentucky, Vol. III., Plate HI, Figs, la, h), 

 which he mistook for the appendages of P. ca2ntalis. The interdistichal 

 plates are large, greatly projecting and angular in the lower portions, while 

 they form deep grooves in the upper. Arms unknown. Column round, 

 narrower than the concavity which it occupies. 



Horizon and Locality. — Kaskaskia group ; Edmonson, Grayson, and 

 Breckenridge Cos., Ky., and Morton Co., Ind. 



Ti/2}e in the Lyon collection. ' ' 



Pterotocrintis acutus Wetheebt. 

 Plate LXXIX. Figs. 3a, b, c, d, e,f, g. 



1879. "Wethebby ; Journ. Cincia. Soc, Nat. Hist., Vol. II. (October No.), Plate 11, Figs. 2«-«. 

 18S1. W. and Sp. ; Revision Palseocr., Part II., p. 91. 



Syn. Ptemtocrhms spatidattis — Wetheebt; Journ. Ciucin. See. Nat. Hist., Vol. II. (October No.), 

 Plate 11, Figs. Za-c. 



Syn. (?) Flerolocrims rui/osiis — Lyon and Cass., 1859 ; Amer. Joum. Sci., Vol. XXIX., p. 71. 



Of the type of F. p//ramidalts Lyon and Cass.; but the basal cup much 

 smaller and the bottom less deeply excavated than in that species, the radials 

 proportionally longer, the anal plate smaller, and the sockets for the recep- 

 tion of the radial appendages wider. The appendages have the shape of a 

 horn terminating in a point instead of an edge. Dorsal cup low basin-shaped, 

 the upper portions flanging outward ; pentangular across the arm bases. 



Basal disk very shallow, rounded at the outer face, not truncate at the 

 bottom, and but slightly excavated. Neither the interbasal nor basi-radial 

 sutures are grooved. Radials short, somewhat irregular in form ; their upper 

 faces moderately concave ; once and a half as wide at the top as at the bot- 

 tom, and twice as wide as long. Anal plate lozenge-shaped, the acute upper 

 angle wedged in between the radials, the obtuse lower angle resting upon the 



