r= 
PLATYCRINID&. (vee 
Platycrinus subspinosus Hatz. 
Plate LXVI. Figs. 9a, b. 
1858. Hanzi; Geol. Rep. Iowa, Vol. L., Part II., p. 536, Plate 8, Figs. 9 and 10. 
1866. Murx and WortHen; Geol. Rep. Ilinois, Vol. IT., p. 178, Plate 15, Fig. 6. 
Smaller than P. discoideus, its dorsal cup has a similar form, but the 
surface of the plates is smooth or very obscurely corrugated; the ventral 
disk shorter, convex instead of pyramidal, and composed of but few large 
plates; the arms heavier, shorter, and without striz. 
Basal disk rather small, broadly and deeply funnel-shaped, the excava- 
tions extending almost to the outer margins. The interbasal sutures very 
slightly grooved, but the basi-radial and interradial sutures deep, and the 
edges of the plates strongly beveled. Radials about once and a half as wide 
as long, and nearly twice as wide at the upper end as at the lower, rising 
very gradually to the facets, which project distinctly outward; the limbs 
curving rapidly upward and slightly inward. The facets, which are not 
thickened around the edges, are directed horizontally, and their faces are 
perfectly flat; they are wider than high and rather large, occupying nearly 
two thirds the width of the plates. Costals very large for the genus, and 
comparatively long; pentagonal; directed outward and slightly downward, 
so that the succeeding distichals are sometimes at a lower level in the speci- 
men than either radials or basals; the upper angle quite obtuse. Distichals 
two; the first quadrangular; the second pentangular; but little smaller 
than the costals, giving off an arm to the outer side of the ray, and two 
palmars to the inner side; the latter supporting an arm to the inner side, 
and two post-palmars to the outer, there being normally four arms to each 
main division and eight to the ray, exceptionally six or seven. Arms heavy, 
moderately short, rounded on the back; composed of rather long, slightly 
convex pieces. They are generally outstretched to about half their length, 
then curve rapidly inward until their tips rest upon the outer margins of 
the tegmen. Disk decidedly quinquelobate, higher than the dorsal cup ; 
the ambulacra highly elevated into ridges. Orals very large, subspinous, 
occupying one half of the ventral surface; rather regular in their arrange- 
ment. Disk ambulacra short, composed of but few tumid pieces. The inter- 
ambulacral spaces small, sometimes formed of a single row of three plates, of 
which the middle one is quite large, the outer ones as long but narrower. 
