240 PALAEONTOLOGY OF ILLINOIS. 



This species, like ScapJiiocrinus simplex of Hall, (Iowa 



Report, vol. i, p. 551) differs in being more robust, and in 



having a more projecting base, while its arms are stouter 



and composed of comparatively shorter and less distinctly 



wedge-formed pieces, which show no lateral projections for 



the support of the tentacles. Again it differs in having its 



first anal piece alternating with two of the subradials, in- 



v3---' a stead of resting upon a truncated upper side of one of them. 



/^CV>Vd l\ Locality and position: Appanoose, Hancock county, 



vvsMw ^'' Keokuk limestone of Lower Carboniferous series. 



Poteriocrinus decadacty- 

 lus. (Nat. size.) 

 Diagram showing the 

 form and arrangement 

 of the basal, subradial, 

 first primary radial and 

 anal pieces, with the sec- 

 ond primary radial, and 

 portions of the arms of 

 the anterior ray. 



Genus ZEACRINUS, Troost. (See page 185.) 

 Zeacrinus planobrachiatus, M. and W. 



PI. 18, fig. 5. 



Zeacrinus planobrachiatus, Meek and Worthen, Sept., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 391. 



Body small, depressed basin-shaped below the summit of the 

 first radials, concave beneath ; composed of apparently smooth 

 plates, connected by moderately distinct sutures. Base small, 

 concave, and apparently nearly hidden by the column. Sub- 

 radial pieces as wide as long, or a little wider, four of them 

 hexagonal, and one on the anal side heptagonal, (counting 

 three angles at the base of each). First radial pieces wider 

 than long, expanding upwards from the base, apparently all 

 pentagonal, the upper side being horizontally truncated, and 

 longer than either of the others. Second radial pieces nearly 

 as large as the first, presenting (in the posterior and lateral 



