PLATYCRINIDJE. 713 



DI8C0IDEUS GROUP. 



Dorsal cnp low basin-shaped, the radials and arras spreading almost 

 horizontally outward ; the arms recurving over the disk. 



Platycrinus dlscoideus 0. and Shum. 



Plate III. Fig.. 17, and Plate LXVI. Figs. 10a, h, c. 



1852. OwiiN and Shumakd ; U. S. Geol. Surv. Wise, Iowa aud Minn., p. 588, Plate 5^, Figs, la, h. 

 1881. W. aud Sp. ; Revision PalEcocr., Part 11., p. 71 (Proceed. Acad. Nat. Sci. Phila., 2i5)° 



Syn. P. corruffattis 0. and Shuji., 1852 ; U. S. Geol. Surv. Iowa, Wise, and Minn., p. 589, Plate 



iA, Figs. ia-e. 

 (not PI, discoideiis Hall, 1858 ; Geol. Rep. Iowa, Vol. I„ Part II., p. 535, Plate 8, Figs, ia, i = 



Encladocfhius pleicrovimmts White). 

 Syn. P. striobrachwtus Hall, 1861 ; Descr. New Spec. Crin., p. 4; also Boston Jonrn. Nat. Hist 

 p. 287 (figured 1872 in Bull. N. Y. State Mus. Nat. Hist., Plate 2, Figs. 2 and 3 (Type in collec- 

 tion of W. and Sp,). Whitfield; Mem. Am. Mus. Nat. Hist., Vol. I, Part I. p 4 Plate 

 3, Figs. 2 to 4. I ' 



Syn. P. muUibmchitttus Meek and Worthen, 1861 ; Proc. Acad. Nat. Sci. Phila., p. 134. 

 Syn. P. simmardianus Hall, 1858; Geol. Rep. Iowa, Vol, I., Part II., p. 532, Plate 8, Fi". 5. 

 _ Syn. P.jtulchellus S. A. Millee, 1891; Geol. Rep. Missouri, Bull. 4, p. 11, Plate 1, Fio-,'?. 



Calyx pyramidal, wider than higli ; 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, witli 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 i\\% curvature, and near the sum- 

 mit alino-st 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 stria3 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 



