518 PALEONTOLOGY OF ILLINOIS. 



gin of one of the irregular shaped subradials, those above are smaller 

 and decrease in size upward. Ventral tube long and apparently cylin- 

 drical (the apex is broken off in our specimen) and composed of small 

 pentagonal plates, crenulated or indented on their margins, giving them 

 a stellate appearance. Column distinctly pentagonal at its junction 

 with the base and for an inch below, which is as far as it can be seen in 

 our specimens. This feature alone will serve to distinguish it fromauy 

 other species known to us from this horizon. 



Position and locality : Alton, Illinois, from the upper division of the 

 St. Louis group, Lower Carboniferous. 



Dedicated to my friend "W. C. Van Horne, Esq., to whom I am 

 indebted for the use of one of the examples figured. 



POTERIOCRINTTS PROBOSdDIALIS, Worthen. 

 PI. 31, Kg. 1. 



Body below the base of the arms depressed obconical, base small, 

 scarcely projecting beyond the circumference of the first columnar 

 joints; basal pieces rather small, nearly twice as wide as high and 

 forming a shallow cup. Subradials, so far as they can be seen on the 

 anal side, a little wider than long and hexagonal; first radial plates 

 about once and a half as wide as high and pentagonal ; second radials 

 a little shorter than the first, quadrangular; third radials as long as the 

 second, pentagonal, and supporting two arms on their superior sloping 

 sides. Anal plates, eight to ten visible, extending up and overlaping 

 or merging into the ventral tube. The two lowest ones are the largest 

 and hexagonal, the succeeding ones growing smaller as far as they can 

 be traced, and all pentagonal or hexagonal. Arms, two to each ray 

 on the anal side, and they appear to bifurcate on the sixth or tenth 

 plate, which is produced laterally into a short, stout spine. Ventral 

 tube nearly two inches long, and apparently a little inflated at its upper 

 extremity, where it is surmounted by three or more short pointed spines. 

 The surface of this organ is ornamented with longitudinal ridges, which 

 seem to be dotted along their upper extremities with minute dimples 

 or oval depressions, and are connected by oblique strise, that give a 

 beautiful cancellated appearance to its surface under a magnifier. Col- 

 umn round, and composed of alternating thin and moderately thick 

 joints, the latter projecting a little beyond the others. 



Position and locality: Carondelet, Mo., in the upper division of the 

 St. Louis limestone, Lower Carboniferous. 



