INVEETEBRATES. 289 



sliping side of the right posterior radial, the second and third are 

 smaller, one resting on the top of the left posterior subradial, and 

 the other on the first anal. 



Column rather stout, the upper joints filling nearly the whole 

 concavity of the base, and composed of thick and thinner joints 

 alternately arranged. 



Position and locality.- Warsaw beds of the St. Louis group, near 

 Clayton, Adams county, 111. 



No. 2,460, Illinois State collection. 



POTERIOCRINUS iLLiNoiENSis, Worthen. 



PL XXVIII, Fig. 17. 



Poteriocrinus Illinoiensis, WORTHEN, Feb. 1882. 

 Bulletin No. 1, of the Illinois State Museum of Natural History, p. 19. 



Body of medium size, obconical, gradually tapering from the sum- 

 mit of the radials to the base. 



Basal plates of moderate size, projecting more than half their 

 length beyond the column, and forming by themselves a low, pen- 

 tagonal cup. 



Subradials as large or larger than the radials, two on the pos- 

 terior side heptagonal, the others hexagonal. 



Eadials rather wider than long, pentagonal, and truncated squarely 

 across their upper margins for the reception of the brachial series. 



Brachials rather smaller than the radials, pentagonal, a little con- 

 stricted above, the upper angle obtuse, and giving support to the 

 first divisions of the rays. The arms are not preserved, in the only 

 specimen yet found of this species, but from the very narrow plates 

 that are to be seen in one of the rays, they probably continue sim- 

 ple above the first division on the brachial series. 



First anal plate longer than wide, pentagonal, and resting be- 

 tween two of the subradials, and partly under the right posterior 

 radial. Second anal larger than the first, hexagonal, and resting 

 on the summit of the left posterior subradial. Third anal smaller 

 than the first, on which it rests, and above this a double series of 

 small plates are partly visible, that probably formed the base of the 

 ventral tube. 



Column round, and near the base composed of joints nearly equal 

 in thickness. 



Geological position and locality: Warsaw beds of the St. Louis 

 group, Warsaw, Illinois. 



No. 2,457, Illinois State collection. 



19 



