Carboniferous Rocks of the Mississippi Valley. 311 



protuberance the tentaciila proceed. These plates are 

 traversed longitudinally by sets of ridges, the central one 

 more prominent and sharply carinate, the lateral ones less 

 distinct. Column proportionally strong, distinctly pen- 

 tangular, composed of equal plates with thin projecting 

 edges. 



This species differs from the two preceding in the propor- 

 tional size of the column, which conceals the basal plates, 

 in havinsf three radials in each series, in the smaller first 

 radials, the more numerous bifurcations of the arms, and 

 the sharply carinated plates. 



Geolog-ical formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collection of Rev. W. H. Bar- 

 ris. 



Scapliiocrimis orbicularis (n. s.) Body below the arms 

 very broadly basin-shaped, or depressed-hemispheric, with 

 the upper margins slightly inflected ; articular scar for the 

 column attachment sharply impressed, extending one half 

 or two thirds the diameter of the basal plates. Basal 

 plates pentagonal, obtusely angular above, forming by 

 their union a pentagon with scarcely concave margins. 

 Sub-radial plates exceedingly large, extending from the 

 edge of the column to near the top of the first radial plates, 

 three sub-pentagonal and two heptagonal (or hexagonal 

 from the straightness of the lower sides), length somewhat 

 greater than breadth. First radial plates proportionally 

 small, sub-triangular ; the lateral edges of the adjacent 

 plates slightly truncating each other. First anal plate 

 large and massive, pentagonal, resting between the two 

 heptagonal sub-radials, and supporting one side of the 

 adjoining first radial plate. The two remaining anal plates 

 (all which are seen in the specimen) are smaller and hex- 

 agonal. 



Arms and column unknown. Surface of plates de- 

 pressed-convex, sutures distinctly marked. The body 



