st oa re ienniaia 
1 —s 
690 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa. 
Type in the (Worthen) Illinois State collection, Springfield. 
Remarks. —'This species was described from a poor specimen, in which 
only the basals and radials were preserved. he markings of the type speci- 
men are less distinct than in the one we figure, but there can be no doubt 
that both belong to the same species. The form and ornamentation of the 
dorsal cup resemble very closely P. brevinedus Hall, from the Keokuk group, 
and it 1s doubtful if the two species are not identical. A satisfactory com- 
parison cannot be made as long as nothing is known of the structure of the 
ventral disk of that species, and in this nothing of the arm structure. 
Platycrinus asper M. and W. 
Plate LX VILL. Figs. 9a, b. 
1861. Merrx and Worrnen; Proceed. Acad. Nat. Sci. Phila., p. 129; also Geol. Rep. Illinois, Vol. III., 
p. 468, Plate 18, Fig. 9. 
1881. W. and Sp.; Revision, Part II., p. 70 (Proceed. Acad. Nat. Sci. Phila., p. 244). 
(Not P. asper Goldfuss = Storthingocrinus asper). 
Below medium size. Dorsal cup twice as wide as high, gradually spread- 
ing, the sides nearly straight; the base depressed, and abruptly and deeply 
excavated so as to form a narrow, thickened rim with an undulating or rough- 
ened surface. A similar rugose rim borders the lower and lateral margins 
of the radials, leaving a small quadrangular depression beneath the facets, 
Sides of the basi-radial and interradial sutures broadly beveled; the inter- 
basal suture lines distinctly grooved. 
Basals rather large, only their outer margins seen in a side view; the 
excavated inner part considerably wider than the diameter of the column. 
Radials wider than long, widening moderately upwards, the lower face 
straight, the outer ends of the upper face slightly sloping; facet semi- 
circular, its width equal to half the width of the plate, and slightly pro- 
jecting. Costals subpentangular, the sloping upper faces concave. Distichals 
once and a half as wide as long, narrower than the costals, and not in con- 
tact laterally. Palmars nearly as large as the distichals and of the same 
general form. Arms of medium size, four to six to the ray —six being 
probably the normal number— composed above the axillaries of sharply 
cuneate pieces, which gradually turn into biserial; the costals, distichals, 
and palmars transversely grooved at the middle. Ventral disk high, bulg- 
ing, composed of rather large, slightly convex pieces; the ambulacral plates 
te 
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