PLATYCRINIDiE. 693 



Platycrinus glyptus Hall. 

 Plate LXVII. Figs. 4, 5. 



1861. Hall ; Descriptions of New Criuoids, p. 16. 



1881. W. and Sp. (var. of P. sculptus) ; Revision, Part II., p. 71 (Proceed. Acad. Nat. Sci. Phila., p. 245). 



As large as the preceding species, and resembling it in the form of the 

 calj-x and style of ornamentation ; but the arms more numerous, more deli- 

 cate, and comparatively shorter. Dorsal cup goblet- shaped, height and width 

 about equal, in very large specimens the height somewhat greater. Surface 

 marked by irregular, undulated ridges or rows of obscure nodes, following 

 the margins of the plates, and increasing in number in the growing Crinoid ; 

 the radials traversed by two diagonal ridges from the facets to the lower 

 angles of the plates. Basi-radial and interbasal sutures canaliculate. 



Basal cup comparatively deep, its height equal to one third the height 

 of the calyx to the arm bases, the lower end rather abruptly truncated 

 and slightly excavated ; interbasal sutures faintly visible. Eadials longer 

 than wide; the lower faces convex — those meeting the interbasal sutures 

 distinctly angular — and slightly beveled along the edges; the sloping upper 

 faces forming a rather deep notch, which at the anal side is twice as wide as 

 at the other sides, and filled by a rather large, lozenge-shaped plate. Eadial 

 facets small, occupying scarcely a third of the width of the plates, and ex- 

 tending but little downward. Costals subtrigonal, moderately large. Dis- 

 tichals twice as wide as long, and not in contact laterally. The higher orders 

 of brachials to the last axillary slightly constricted in the middle, and gradu- 

 ally decreasing in width but retaining the same length, so that the upper 

 ones are as long as wide, and even longer in young specimens. Arms rather 

 delicate and short for the size of the species; they are very numerous, there 

 being from six to seven to each division of the ray, or twelve to fourteen to 

 the ray, the bifurcations extending to fully one half the length of the arms, 

 and above the palmars given off from the third plate. Structure of ventral 

 disk and anus unknown. Column rapidly twisting ; the two or three prox- 

 imal joints circular, the others elliptic, increasing in length downward ; the 

 long diameter of the joints fully twice the shorter one. 



Horizon and Locality. — Upper Burhngton limestone; Burlington, Iowa, 

 and Henderson Co., Ill, 



