- 4 “23 = ~ A 4 fy es - owe s oe — 7 ~ = e aha - 4 a 
4 as - eee eee - & Oe eh om » 2 = é =5 ‘“ : = Z a x ra 
z Be Ie of. ae Ss Vaasa” 8 8 SS AS 2 eee ee ee ee ee ee ee 
PLATYCRINID&. 713 
DISCOIDEUS GRhOUP. 
Dorsal cup low basin-shaped, the radials and arms spreading almost 
Lauzon outward; the arms recurving over the disk. 
Platyerinus discoideus O. and Sxum. 
Plate III. Fig. 17, and Plate LX VI. Figs. 10a, 6, ¢. 
1852. Owen and SHumarp; U. S. Geol. Surv. Wisc., Iowa and Minn., p. 588, Plate 5.4, Figs. la, 0. 
1881. W. and Sp.; Revision Paleocr., Part II., p. 71 (Proceed. Acad. Nat. Sci. Phila., 245). 
Syn. P. corrugatus O. and Suum., 1852; U.S. Geol. Surv. ee Wisc. and Minn., p. 589, Plate 
5A, Figs. Qa-e. 
(not Pl. discoideus Hatt, 1858; Geol. Rep. Iowa, Vol. I., Part IL, p. 535, Plate 8, Figs. 8a, d= 
Hucladocrinus eee White). 
Syn. P. striobrachiatus Hatt, 1861; Descr. New Spec. Crin., p. 4; also Boston Journ. Nat. Hist., 
p. 287 (figured 1872 in Bull. N. Y. State Mus. Nat. Hist., Plate 2, Figs. 2 and 3 (Type im collec- 
tion of W. and Sp.). Whitfield; Mem. Am. Mus. Nat. Hist., Vol. I., Part I., p. 4, Plate 
3, Figs. 2 to 4. 
Syn. P. multibrachiatus Munx and WortueEn, 1861; Proc. Acad. Nat. Sci. Phila., p. 134. 
Syn. P. shumardianus Hatt, 1858; Geol. Rep. Iowa, Vol. I., Part II., p. 532, Plate 8, Hig. 5. 
Syn. P. pulchellus 8. A. MittER, 1891; Geol. Rep. Missouri, Bull. 4, p. 11, Plate 1, Fig. 7. 
Calyx pyramidal, wider than high; the dorsal cup discoid, almost flat 
to the middle of the radials, then curving rapidly upwards until the limbs, 
which rise far above the top of the facets, stand at right angles to the plane 
of the base. Plates covered by well defined corrugations, which in some 
specimens are gathered into imbricating folds covering the whole surface ; 
in others arranged in concentric lines conformable to the sides of the plates. 
Base pentagonal, with a deep concavity in the centre, slightly convex toward 
the outer margins. Column facet circular; the interbasal sutures invisible. 
Radials almost as long as wide, allowing for the curvature, and near the sum- 
mit almost twice as wide as at the base. Radial facets large, lyre-shaped, the 
vertical diameter equal to one half the length of the plates; the lower rim 
projecting and on a level with the basals. The surface of the facets concave, 
and covered with fine radiating stris without other markings. Basi-radial 
and interradial sutures deeply grooved, the edges of the plates strongly 
beveled. Costals triangular, occupying the full width of the facet. Dis- 
tichals and palmars twice as wide as high. Arms from six to eight to 
the ray; one subdivision in the same specimen may have but three arms, 
the other four and exceptionally five. The arms are rather stout, simple 
and biserial, and are finely striated longitudinally. Disk almost three times 
90 
’ as - 
Fe 2 ET 
