PLATYCRINIDiE. 695 



laterally. Column observed to a length of 29 cm. without showing cirri. 

 The joints change rapidly from circular to elliptical, and in width from 7 mm. 

 to 17 mm. within 40 mm. from the crown, and from 1 mm. to 3 mm. in 

 length. Their outer margins are angular, and the middle portions covered 

 with a transverse row of ill-defined nodes. 



Horison and Localitxj. — ■ Upper Burlington limestone and Keokuk group ; 

 Indian creek, Montgomery Co., Ind. ; Keokuk, Iowa, and throughout Ken- 

 tucky, Tennessee, Illinois, and Missouri, at the same geological horizons. 



Tijioe in the (Worthen) Illinois State collection, Springfield. 



Memarhs. — In a paper on " Transition forms in Crinoids " (Proceed. 

 Acad. Nat. Sci. Phila., 1878, p. 244), we made this and the preceding species 

 varieties of P. sculi^tus. They agree so closely in the form of the dorsal cup, 

 and in the style of ornamentation, that it is impossible to separate them 

 unless the arms are preserved, and even these do not differ essentially except 

 in number. We now rank them as full species, but believe that P. glyptus 

 and P. Scifordi are lineal descendants of P. sculjitus, 



Platycrinus seobina M. and W. 

 Plate LXVIII. Figs. Ua, b. 



1S61. Meek and Woktheu; Proceed. Acad. Nat. Sci. Pbila , p. 129; also Geol. Rep. Illinois, Vol, III., 

 p. 466, Plate 16, Fig. 9. 



ISSI. W. and Sp. ; Revision, Part II., p. 75 (Proceed. Acad. Nat. Sci. Pliila., p. 249). 



Sjn. Piati/criiius clt/tis — 'H.iLL, 1S61 ; Prelim. Descr. New Spec. Crin., p. 4; also Boston Journ. 

 Nat. Hist., Vol. VII., p. 286; figured 1873, N. Y. State Mus. Nat. Hist., Bull. 1, Plate 2 J, 

 Pig. 4, and Mem. Am. Mus. Nat. Hist., Vol. I., Part I., p. 2, Plate 3, Pig. 6. 



A small species. Dorsal cup basin-shaped, more than once and a half as 

 wide as high, the radials slightly convex, especially below the facets, giving 

 to the transverse section of the cup an obscurely pentangular outline, and to 

 the interradial sutures a shallow angular depression. Surface of cup orna- 

 mented with numerous small nodes or coarse granules, rather sharply 

 elevated, closely set, and irregularly arranged, which produce a rasp-like 

 appearance. 



Basals closely anchylosed, leaving no groove or mark ; they form a 

 rounded basin, which rises to two fifths the height of the dorsal cup ; the 

 column facet small, and almost on a level with the truncated lower face. 

 Radials a little broader than long, widening somewhat upwards, and present- 

 ing a subquadrangular outline; the superior faces almost straight, their 

 outer ends being but very slightly truncated. Radial facets small, occupying 



