FOSSILS OF THE CHESTER GROUP. 549 



once arid a half as wide as high, all pentagonal, convex, 

 but not protuberant. First anal piece about once and a 

 half as long as wide, pentagonal and protuberant. Second 

 and third anal pieces smaller than the first, hexagonal and 

 pentagonal, and both strongly convex. Surfaces of all the 

 plates without ornamentation. Arms and column un- 

 known. 



Locality and position Chester division of the Lower Carboniferous 

 series : Day City. Pope comity, Illinois. 



ZEACRESUS FOKMOSUS, Worthen Ms. 



PI. 521, Fig. 2. 



BODY of medium size, depressed basin shaped, and a 

 little more than twice as wide as high. Base small, and 

 impressed for the reception of the column ; the first column 

 joint covering about one half the length of the small basal 

 pieces. Sub-radials about as wide as long, three hexagonal 

 and two heptagonal ; all curving inward at their lower ex- 

 tremities, to form the concavity of the base. First radials 

 about once and a half as wide as long, all pentagonal except 

 the one on the right of the first anal piece, which appears 

 to have but four angles, and, with the first anal curves 

 abruptly inward on its upper margin. Second radials pen- 

 tagonal, nearly as long as the first, and on three of the 

 rays seen give origin on their upper sloping angles to two 

 arm pieces in each ray. Surface of all the plates finely 

 lirannlose and convex, but not protuberant. 



Locality and position. Chester division of the Lower Carboniferous 

 serk-s . Chester, Illinois. 



