ECHINODERMA TA—CRINOIDEA . 



537 



one and one half inches wide across the arm bases). General out- 

 line and surface of plates as in P. tennesseensis, but calyx con- 



FlG. 1865. Periechocrinus tennesseensis (center) ; P. ornatus (sides). Pal. Ohio. 



stricted below the arm bases. Arms four to the ray, in pairs. 

 Anus subcentral on a protuberance which terminates an anal ridge. 

 Tegmen almost flat. 

 Niagaran of Illinois. 



122. P. (Saccocrinus) ornatus (Hall). 

 (Fig. 1865.) Siluric. 



Distinguished by the large anal tube. 

 Niagaran of Ohio and Indiana. 



123. P. (Saccocrinus) tennesseensis (Hall) . 

 (Fig. 1865.) Siluric. 



Primary arms 20. Arm bases conspic- 

 uously projecting, with deep depressions be- 

 tween the rays and their main divisions 

 which are deepest on the anal side. Lon- 

 gitudinal elevation of radial series faint. 



Niagaran of Tennessee and Ohio. 



124. P. whitei (Hall). (Fig. 1866.) 

 Plates unornamented except for a faint radial ridge. 

 Kinderhook and Burlington of Iowa. 



Fig. 1866. Periechocri- 

 nus whitei, a small speci- 

 men. (After Meek and 

 Worthen. ) 



Mississippic. 



