CRINOIDS. 195 



marked by broad, angular ridges, extending from one plate to 

 another and becoming somewhat depressed as they cross the 

 sutures; these ribs are rendered more prominent by the exca- 

 vated corners of each ossicle. Ventral pieces more or less 

 conspicuously spinous. 



Horizon and localities. — Lower Carboniferous, Lower Bur- 

 lington limestone : Kinderhook ( Illinois) ; Burlington ( Iowa). 



Steganocrinus pentagonus (Hall). 



Plate xxiv, fig. 9. 



Adinoerinus pentagonus Hall, 1858: Geol. Iowa, vol. I, p. 577, pi. X, figS. 



6a-b. 

 Steganocrinus pentagonus Meek & Worthen, 1866 : Geol. Sur. Illinois, vol. 



II, p. 198. 



Steganocrinus pentagonus Meek & Worthen, 1868 : Geol. Sur. Illinois, vol. 



III, p. 474, pi. xvi, fig. 8. 



Calyx of medium size, about as broad as high, somewhat 

 stellate, with the general arrangement of the ossicles as in Ac- 

 tinocrinus, but radially produced into long, slender, cylindrical 

 extensions, from which a large number of free arms are given 

 off. Surface of the dorsal cup ornamented by rather well-de- 

 fined ridges running from the center of each plate, where they 

 form an indistinct nodosity, to the centers of the adjoining ossi- 

 cles ; ventral pieces nearly smooth except toward the base of 

 the anal tube, where they become spinous. 



Horizon and localities. — Lower Carboniferous, Lower 

 Burlington limestone: Louisiana. 



Platycrinus brlttsi Miller. 



Platycrinus brittsi Miller, 1891: Geol. Sur. Missouri, Bui. 4, p, 23, pi. iii, 

 figs. 3-4. 



Calyx cup-shaped, ilattened below ; plates smooth ; basals 

 less than one-fourth the height of the dorsal cup; radial 

 about as wide as high. 



Horizon and localities. — Lower Carboniferous, Chouteau 

 limestone : Sedalia. 



Platycrinus ollicula Miller. 



Platycrinus ollicu la Miller, 1891 : Geol. Sur. Missouri, Bui. 4, p. 19, pi. 11$ 

 figs. 7-8. 



