OBINOIDS. 185 



Genus Actinocrinus Millkr. 



Calyx top-shaped, more or less distinctly pentalobate ; 

 dorsal cup usually sculptured by promineat ridges ; ventral 

 side convex, with a long anal tube. Basals three in number, 

 equal, flattened below. Eadials very large, usually higher than 

 wide ; first costals somewhat smaller, hexagonal, about as long- 

 as wide ; second costals still smaller than the first, pentagonal ; 

 distichals similar to the second costals : subsequent orders of 

 calyx brachials variable in number, according to the number of 

 arms ; arms biserial, ranging from 20 to 60 or more, long, rather 

 robust, with ends somewhat turned inward: pinnules long, 

 laterally compressed ; joints rather long, each armed with a 

 hooked spine. Anal plate very large, similar to and in line 

 with theradial8,and supporting two ossicles in the second row. 

 Interradials usually about three in number and of nearly equal 

 size, but often followed by smaller pieces. Ventral side formed 

 of rather large plates, some of which are somewhat nodose. 

 Anal tube subcentral, long, stout, often extending beyond the 

 tips of the arms. Column long, rather heavy ; central canal of 

 medium size. 



Actinocrinus is one of the most important genera of the 

 Lower Carboniferous, and is the type of a large number of 

 forms which are more or less closely related to it. 



Actinocrinus proboscidialis Hall. 



Plate xxiv, fig. 1. 

 Actinocrinus proboscidialis Hall, 1858: Geology lowa, vol. I, p. 584, pi. x, 



fig. 13. 

 Actinocrinus quaternarius Hall, 1860: Geol. lowa, vol. I, Supp. p. 22. 

 Actinocrinus quaternarius , v&T. spinifet'tis Hall, 1861: Desc. New Pal. Cri- 



noids, p. 11. 

 Actinocrinus themis Hall, 1861: Desc. New Pal. Crinoids, p. 11. 

 Actinocrinus lagina Hall, 1861 : Desc. New Pal. Crinoids, p. 13. 

 Actinocrinus proboscidialis Keyes, 1890: Am. Naturalist, vol. XXLV, p. 



254, pi. viii, fig. 2. 



Crown subcylindrical. Calyx turbinate, somewhat conical 

 above. Column long, rather heavy, with well-defined nodal 



G— 13 



