PALEONTOLOGY OF IOWA. 



545 



Another individual* from Chester ( Illinois), which I have received under the 

 designation of Zeacrinus magnolia formis , has a narrower and less rotund base, with 

 the cavity much less deep, and the subradial and first radial plates proportionally 

 shorter and the latter narrower; while the anterior ray has two intermediate radial 

 plates, with other slight differences in the bifurcation of the arms. 



The accompanying diagram (fig 65) will il- 

 lustrate the characters mentioned, and also show 

 the relations of the anal plates. The parts within 

 the circular line in this and the preceding figure 

 are those occupying the exterior depression or 

 cavity of the base. 



In the Cyathocrinus dcpressus, TROOST (the basal and first radial portions known), 

 which is a species of the Genus ZEACRINUS, the proportions of the parts are stili 

 more extravagant. In one specimen, the five small plates of the base are shown in he 

 bottom of the very abrupt basal depression; while the subradial plates assume a 

 spatulate form, except on the anal side, where the subradial is truncated above, and 

 a large anal is inserted on one side reaching far into the cavity of the base. 



in a deep cavity, and is supported by a cylindrical column having a circular alimentary 

 canal. The cavity being mostly filled by the column, the form and even the existence of 

 the pelvis is very uncertain. Costals five, subtriangular, tumid; superior margin concave, 

 and lower convex; and being bent inwardly, they form the base of the body and the 

 sides of the cavity, in the bottom of which the pelvis? is situated. Scapulars five, com- 

 pressed, pentagonal; four of them being placed immediately upon the concave surface 

 of the costals, and one upon an interscapular, the superior margin being cuneiform. The 

 scapulars support five arms, upon which follow immediately ten hands, which, after two 

 or three joints, have a cuneiform j oint dividing them into two fingers, one of which con- 

 tinues single; while the others, about five joints distant, bifurcate again, and continue 

 then without any further division". 



* This is apparently a species distinct from Z. magnoliaformis , with shorter first ra- 

 dials extending little above the plane of the base, and arms much shorter and less robust ; 

 for which I propose the name Zeacrinus wortheni. 



[ IOWA SURVEY.] 



69 



