HEXACRINIDE. . 799 
which in this species do not penetrate the test, but rest exclusively against 
the sloping faces of adjoining plates. The anal side has two interambulacral 
pleces 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 plates. 
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. Rep. Kentucky, Vol. III., Plate IIL, Figs. 1a, 3), 
which he mistook for the appendages of P. capitalis. 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. 
Type in the Lyon collection. 
Pterotocrinus acutus WETHERBY. 
Plate LX XIX. Figs. 3a, b, ¢, d, e, f, g. 
1879. WetHErsy; Journ. Cincin. Soc. Nat. Hist., Vol. II. (October No.), Plate 11, Figs. 2a-c. 
1881. W.and Sp.; Revision Paleocr., Part IT. p. 91. 
Syn. Prerotocrinus spatulatus — WetuHERBY ; Journ. Cincin. Soc. Nat. Hist., Vol. II. (October No.), 
Plate 11, Figs. 8a-c. 
Syn. (?) Péerotocrinus rugosus — Lon and Cass., 1859; Amer. Journ. Sci., Vol. XXIX., p. 71. 
Of the type of P. pyramidalis 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 
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