Carboniferous Rocks of the Mississippi Valley. 297 



somewhat turbinate, base broadly truncate and surrounded 

 by a somewhat large rim formed by the thickening of the 

 basal plates. Basal plates proportionally large, pentago- 

 nal, angular above. Sub-radial plates minute, sub-hexag- 

 onal, the two adjoining the anal plate differing from the 

 others in form. First radial plates much larger than the 

 succeeding ones, wider than high, the upper lateral angles 

 strongly incurved, giving the plate a sub-heptagonal form. 

 Second and third radial plates sub-quadrangular, wider 

 than high. Fourth radial plate pentagonal, angular above. 

 The rays are free above the first radial plates. 



Arms originating on the fourth radial plate, without 

 true bifurcations above, but sending off branchlets from 

 the opposite sides alternately ; these, like the arms, are 

 composed of short plates, alternately longer and shorter 

 on the opposite sides, except near the arm base, where 

 they are more equal. First anal plate minute, pentangu- 

 lar, resting upon one basal plate and between two sub- 

 radial plates, partially supporting one first radial and the 

 second anal plate ; this is sub-heptagonal, nearly two 

 thirds as large as the first radial. The third and fourth 

 anal plates little smaller than the second, form not deter- 

 mined. Surface of plates ii-regularly nodose ; on the sub- 

 radials the nodes are high, and occupy almost the entire 

 plate. The first radial plates are marked by two strong 

 ridges, which, passing down from the upper margin, unite 

 with ridges from the adjacent sub-radial. Column at its 

 junction with the body pentalobate. 



This species is distinguishable by peculiarities in the ra- 

 dial series and the arms. The radial plates are concave 

 above and convex below, elevated along the middle and 

 depressed at the sides, presenting an appearance of some 

 species of Forbesicrinus. The plates of the lower part of 

 the arms are also peculiar. 



Geological formation and locality. Burlington lime- 



JOURNAL B. S. N. H. 3& 



