Carboniferous Rocks of the Mississippi Valley. 265 



Arms proportionally strong, round at the base, and be- 

 coming somewhat flattened above ; composed of a double 

 series of interlocking plates, armed at their outer edges 

 with short, spine-like nodes. Proboscis strong, composed 

 of small plates. Column of medium size, composed of 

 short, alternately thicker and thimier plates, ornamented 

 on the margins. 



This species is of the type of A. mnltibrachiatus ; but 

 differs from that and all other described species in the or- 

 naments of the surface, the crowded horizontal brachial 

 plates, and flattened arms. In this latter character it re- 

 sembles A. clio, but differs materially in form of body and 

 arm formula. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collection of C. A. White of 

 Burlington. 



Actinocrinus corhulis (n. s.). Body broadly caliculate ; 

 dome highly convex, sub-hemispherical, surmounted by a 

 sub-central proboscis. Basal plates short, with strongly 

 projecting lower margins, slightly indented at the suture 

 lines. First radial plates short, twice as wide as high. 

 Second radials very small. Third radial plates very small, 

 obtusely wedge-form above, supporting on each upper edge 

 a series of two supra-radial plates, the upper ones of which 

 support on the upper inclined edges the brachial plates ; 

 two of these contribute to the form of the body or calyx. 

 Brachial formula n = 20. 



Interradial series consisting of from one to three plates 

 each. First anal plate heptagonal, higher and narrower 

 than the first radial plates, supporting three anal plates 

 above in form of an arch. Surface of plates slightly con- 

 vex, the interradials a little depressed. The brachial 

 spaces are somewhat impressed, giving a slightly lobed ap- 

 pearance at the arm bases. Dome composed of nodose 

 plates, the three above each ray large and distinctly tuber- 



JOtTRNAL B. S. N. H. 34 JAXUAUY. 1861. 



