198 PALAEONTOLOGY OF ILLINOIS. 



extraordinary differences in the other parts, will adopt this genus. Believing 

 as we do, however, that the whole combination of characters presented by the 

 entire structure of these animals should be taken into consideration in their 

 classification, we can but regard the differences between this type and the typi- 

 cal forms of Actinocrinus as being of generic importance. 



At present we know of but three species that can be with any degree of con- 

 fidence referred to this group. These are the typical species, S- pentagonus= 

 (Actinocrinus pcntagonus, Hall), S. sculptus=(Act. sculptus, Hall), and our 

 S. araneolus, first described by us as Actinocrinus araneolus. We have little 

 doubt, however, but several other species referred to the genus Actinocrinus, 

 from our Carboniferous rocks, will be found to belong here. 



So far as known, this group is confined to the Subcarboniferous rocks of 

 America. 



Steganocmnus akaneolus, M. and W. 



PI. 15, Fig. la, IS. 



Actinocrinus araneolus, Meek and Worthen, Sept., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 387. 



Body small, much depressed, stelliform as seen from above 

 and below, in consequence of the deeply excavated character 

 of thje interradial spaces; composed of obscurely granulose 

 plates, which are more. or less distinctly costate and angular 

 on the under side of the body. Base small, flat, and subhex- 

 agonal; columnar facet round and nearly flat. First radial 

 plates extending out horizontally on a plane with the base, 

 strongly convex and angular in the middle, from which a more 

 or less prominent angular ridge radiates to each of the sides; 

 all slightly broader than long, and hexagonal or heptagonal, 

 the central angle at the base of the latter being very obtuse. 

 Second radial pieces nearly as large as the first, wider than 

 long, distinctly curved upwards at each side, and more or less 

 convex in the middle, from which an obscure angle sometimes 

 extends to the side, connecting with the base, and one to each 

 of the lateral margins, presenting a hexagonal outline as seen 

 from below, but possessing an additional angle on each side, 



