200 PALAEONTOLOGY OF ILLINOIS. 



measuring across between the rays, 0.45 inch; height of ditto, 

 0.32 inch ; breadth of free rays before bifurcation, 0.14 inch; 

 breadth of the divisions of ditto, at the base, 0.10 inch; breadth 

 of proboscis at base, 0.17 inch. 



This species is most nearly allied to S- pentagonus, but will be readily distin- 

 guished by its smaller size and much more depressed form. This difference of 

 form is most obvious in a side view, its base being truncated so as not to be 

 seen projecting beyond the subradials, upon which the body rests when placed 

 on a plane surface in its natural attitude. 



Locality and position: Burlington limestone, of the Subcarboniferous series, 

 Burlington, Iowa. 



Genus ACTINOCRINUS, Miller, 1821 (page 147). 

 Actinocrinus concinnus, Shumard. 



PL 15, Pigs. 9a,*9 5. 



Actinocrinus concinnus, Shumard, 1855. Missouri Report, plate A, figure 5. 

 Actinocrinus validus, Meek and Worthbn, Sept., 1860. Proceedings Acad. Nat. Sci., 

 Philad., p. 384. 



Body of medium size, subglobose in form, exclusive of the 

 third radial and secondary radial pieces, the summit being more 

 depressed than the cup below the arms. Calyx beneath the 

 top of the second radial plates, somewhat rounded on the sides, 

 and composed of thick, convex, radiately costate plates, con- 

 nected by moderately distinct sutures. Summit composed of 

 smaller irregular tuberculose pieces, and provided with a nearly 

 central proboscis ; anal and interradial spaces deeply sinuous. 

 Base small, truncated and slightly concave below, about four 

 times as wide as high, not provided with a continuous marginal 

 rim, composed of nearly equal plates, with deeply grooved 

 sutures between ; columnar facet nearly two thirds as broad as 

 the base, concave and marked by fine, radiating strise. First 

 radial plates generally a little wider than high, two of them 

 hexagonal, and three heptagonal, the angle at the middle of 



