— 
TI 
St el 
nN eee 
796 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
and form irregular trihedrons with undulating faces and rounded angles, the 
side by which they are attached to the calyx touching with one end the 
orals, and with the other the plates of the dorsal cup. The median part of 
the tegmen (the nucleus of the star) is concave, except its posterior side, 
which is slightly raised by the anal structures, which occupy fully one third 
of the central space. Anal opening subcentral; surrounded by numerous 
small plates, which are enclosed by larger ones of irregular arrangement. 
The orals vary in size as well as in form; the posterior one, which is wedged 
In between the others, is pushed over to the anterior side; it is rather small, 
slightly convex, and subtrigonal in outline, though actually pentagonal; the 
two anterior orals are larger than the lateral ones. The extreme outer ends 
of the orals are bent abruptly downward so as to produce, together with the 
depressed inner ends, sharp edges, which connect with the projecting mar- 
gins following the appendages, forming with them a well defined rim around 
the whole upper surface of the calyx. The spaces between the appendages 
are placed at right angles to the upper face; they are subtriangular in out- 
line, and distinctly grooved for the reception of each separate arm. At the 
four regular sides there are apparently six interambulacral pieces, and prob- 
ably eight at the anal side. 
Horizon and Locality. — Kaskaskia group; Crittenden Co., Ky, 
Type in the Lyon collection, Jeffersonville, Ind. 
Pterotocrinus depressus Lyon and Cass, 
Plate LX XIX. Figs. 2a, b, ¢, d, e. 
1859. Lyon and Cassepay; Amer. Journ. Sci., Vol. XXIX., p. 68. 
1866. Suumarp; Trans. St. Louis Acad. of Sci., Vol. IL. p. 394. 
1873. Muenx and Wortuen; Geol. Rep. Illinois, Vol. V., p. 559, Plate 21, Figs. 18, 18a-c. 
1881. W. and Sp.; Revision Paleocr. Part II., p. 91. 
This species is distinguished from all others by its enormous, flat, knife- 
like appendages, and by the position of the anus, which occupies the top of 
a central slender cone. Calyx a little higher than wide; the dorsal cup 
shorter than the ventral disk, depressed bowl-shaped; the sides straight or 
slightly convex; the lower portions rounded. Plates smooth and the suture 
lines rather indistinct. 
Basals of moderate size, but very slightly projecting, with a shallow con- 
cavity at the bottom, which is completely filled by the column. Radials 
irregularly pentagonal, the sides rapidly spreading, especially those facing 
