530 PALEONTOLOGY OF ILLINOIS. 



plates five or six deterininable, and all apparently hexago- 

 nal. Arms composed of a single series of wedge-formed 

 pieces, two to each ray, bifurcating first on the fourth or 

 sixth piece, and again on the eighth, and some of the 

 branches bifurcate a third time on the sixth or eighth 

 piece. The anterior ray bifurcates only once, apparently 

 about the eighth piece above the second radial. 



Some indications of an inflated ventral tube may be seen, 

 not quite as long as the arms, the apex of which is formed 

 of spiniferous plates. 



Locality and position Same as the last. 



This species is nearly related to Z intermedius, Hall, but differs in 

 the ornamentation of its body plates and in the mode of bifurcation of 

 its arms. 



ZEACRINUS COMPACTILIS, Worthen Ms. 



PI. 21, Fig. 5. 



BODY of medium size, and to the top of the first radial 

 pieces forming a nearly flat pentagonal disc. Base a little 

 concave, the basal pieces partly hidden by the first colum- 

 nar joint. Subradials very small, pentagonal and hexago- 

 nal, and deeply inserted between the first radials. First 

 radial pieces comparatively large, nearly twice as wide as 

 long, four hexagonal and one pentagonal, and truncated 

 entirely across their upper margins for the reception of the 

 second radials. Second radial pieces nearly as large as the 

 first, and all but the one on the anterior ray with their up- 

 per angles produced into a prominent obtuse point, or node, 

 against and partly upon which the third radial pieces rest. 

 Third radials on four of the rays about twice as wide as 

 long, and two to each ray, giving origin to two arms com- 

 posed of very thin, flat, nearly circular pieces, of which 

 there are from four to six in each arm. These are suc- 

 ceeded by a thick protuberant axillary piece like the second 

 radials, (except that the nodes upon these point outward 



