192 



PALAEONTOLOGY OF ILLINOIS. 



So far as known to us, this group is confined to the horizon of the Burling- 

 ton limestone of the Subcarboniferous series, and unless Actinocrinus costus, of 

 McCoy, from the Carboniferous rocks of Ireland, may possess the expanded 

 summit of this genus, it would seem to be peculiar to America. 



Strotocrinus regalis, (sp.) Halt! 



PI. 16, figs. 6a, 66, and following cut. 



Actinocrinus regalis, Hall, 1860. Sup. Iowa Report, p. 8. 



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

 Philad., p. 386. 



Fig. 7. 



Strotocrinus regalis. — (Nat. size.) . 

 Side view, showing the body with part of the expanded summit broken away. When 

 entire, the expanded summit extended out at least as far as indicated by the dotted lines. 



Body attaining a large size, elongate obconic below the hori- 

 zon of the arms; composed of moderately convex, ornately cos- 

 tate plates, which are joined by more or less impressed sutures. 

 Base, cup or basin-shaped, twice as wide as high, truncated 

 below, for the reception of the column, and expanding mod- 

 erately upwards — composed of regular, subequal, hexagonal 

 plates, with broadly and deeply grooved sutures; facet for the 

 reception of the end of the column flat, rather large, or nearly 

 half as broad as the summit of the base, marked by radiating 



