286 PALEONTOLOGY OF ILLINOIS. 



POTEBIOCEINUS FouNTAiNENSis, Worthen. 



PI. XXX, Fig. 11. 



Potericrinus Fountainensis, WORTHEN, February, 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 17. 



Body under medium size, rapidly spreading from the base to the 

 top of the radial series, where it is about twice as wide as high. 

 Basals small and concealed by the first columnar joints. Subradials 

 hexagonal and heptagonal, length and breadth about equal. Eadials 

 once and a half as wide as long, pentagonal, with a well defined 

 suture between them and the brachial plates. Brachials about twice 

 as long as wide, pentagonal, and narrower in the middle than at the 

 ends and supporting two arms on their upper sloping sides, the 

 brachial on the anterior ray being longer and more constricted than 

 the others. Arras apparently but two to the ray, and composed of 

 long zigzag joints, constricted in the middle and giving off on alter- 

 nate sides from their upper angles strong pinnules, that are about 

 half as large in diameter as the arms. 



The first anal plate is nearly quadrangular in form, and rests be- 

 tween two of the subradials and under the left side of the right pos- 

 terior radial. The second and third are a little smaller than the first, 

 and above these there is a double series of small plates that extend 

 up to the base of the ventral tube. 



This species is rather closely related to Pot. (Scaph.) internodius, 

 of Hall, Iowa Report, part 2, but differs from that in the form and 

 proportions of the plates of the body, and in the zigzag arrangement 

 of the arms. 



Position and locality: St. Louis limestone, Fountain creek, Monroe 

 county, Illinois. 



No. 2,4c5, Illinois State collection. 



NOTE. The Scap7iiocrinus decabrac Hiatus, 8. internodius, S. scoparius andZeacri/n/x 

 intermedius, described by Hall in the Iowa Report, part 2, were collected by the writer, 

 and were all from the St. Louis limestone and not from the Chester group, a fact that it 

 is necessary to bear in mind in the identification of these species with those from other 

 localities. 



