PALEONTOLOGY OF IOWA. 567 



latus ; while Ag. stellatus, a little farther removed from that type, shows faintly the 

 basal plates projecting beyond the column. 



Fig. 1 a. Anterior side of specimen. 



Fig. 1 b. The anal side of specimen. 



Fig. 1 c. The base, showing the narrow rim of basal plates surrounding the column, 

 and the first radial plates in the same plane. 



Geological formation and locality. In the Burlington limestone : Bur- 

 lington, Iowa. 



Actinociinas brevis ( n. s.). 



PLATE X. FIG. 3 a, b. 



BODY vertically depressed, convex above, flattened or 

 scarcely convex below, concave in the centre ; the basal 

 plates hidden by the column. First radial plates hexagonal 

 (the base following the curve of the column), longer than 

 wide. Second radials small, quadrangular. Third radials 

 small, pentagonal, succeeded by two or more brachial plates 

 from each upper oblique side. First interradials ten-sided, 

 supporting two long, narrow second interradials which 

 lie between the bases of the arms, and are more properly 

 interbrachials. Arms double from their origin, or two from 

 each radial, giving ten arms at the base. First anal plate 

 large, and supporting three other large plates of heptagonal 

 form ; and above these, six ranges of small plates below the 

 anal opening, which is separated from the apicial plate by 

 two ranges of small plates. Superaxillary plates prominent, 

 about two or three in a line from the arm to the centre. 

 Summit composed of numerous small plates : apicial plate 

 elevated into a rounded tubercle. All the plates below the 

 arms with short abrupt ridges at the lines of junction. Sur- 

 face granulose. 



In the flattened base, absence of visible basal plates, and elongation of some of 

 the plates, this species approaches the character of AGARICOCIUNUS : in aspect it also 

 resembles it, in the depressed summit and incipient tuberculose plates. It differs 

 sufficiently from any species of this formation, to be readily distinguished. 



Fig. 3 a. Anal side of the specimen. Fig. 3 b. Basal view of the same. 



Geological formation and locality. In the Burlington limestone : Bur- 

 lington, Iowa. 



