802 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
often altogether hidden from view. Distichals and lower arm plates nearly 
of equal size. The arms free from the second plate, and biserial from the 
fourth; they are unusually strong, rounded at the back, and composed of, 
two rows of short, transverse pieces. Pinnules slender and closely arranged. 
The appendages are thin and knife-like at their upper edges, much thicker 
below (Meek and Worthen) than above. Construction of the ventral disk 
unknown. Column round, occupying about one fourth of the basal concavity. 
Horizon and Locality. — Kaskaskia group; Hardin Co., Ils. 
Type in the Illinois State collection, Springfield. 
Pterotocrinus chesterensis Mrrex and WorTHEN. 
Plate LXXIX. Figs. da, b. 
1860. Dichocrinus (Pterotocrinus) chesterensis —Munx and Wortuen; Proceed. Acad. Nat. Sci. Phila. 
p. 388. 
1866. Péerotocrinus chesterensis —MuEK and Wortusn; Geol. Rep. Illinois, Vol. II., p. 292, Plate 23, 
Figs. la, 3, ¢. 
1881. Pterotocrinus chesterensis —W. and Sp.; Revision Paleocr., Part II., p. 91. 
The smallest known species of the genus. Sides of the dorsal cup dis- 
tinctly concave, rapidly spreading upwards; the base truncated, and its lower 
margin projecting; the plates without ornamentation, and the suture lines 
not grooved. 
Basal cup about one third the width of the calyx at the arm bases, and 
about three times as wide as high, truncated and concave below, the concav- 
ity surrounded by an angular rim. Radials not quite twice as wide as long, 
widening rather rapidly from below, the superior faces a little excavated 
except the outer ends, which are slightly truncated. Costals small, trian- 
gular. Distichals irregularly pentagonal. Fixed palmars four; the two 
outer ones in the same line with the distichals, and lke them reposing upon 
the radials. Anal piece subovoid, its broadest end about as wide as the 
radials at their lower faces, the upper end angular. Arms biserial from the 
third plate up, small, and rounded on the back. Structure of ventral disk 
and form of the appendages unknown. 
Horizon and Locahty. — Kaskaskia group; Hardin Co., Ills. 
Type in the (Worthen) Illinois State collection, Springfield. 
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