PALEONTOLOGY OF IOWA. 571 



partially developed. Arms four from each ray on either side 

 of the anal space, and three from each of the other radials, 

 making altogether seventeen. Surface, in perfect specimens, 

 somewhat strongly granulose striate. 



This species differs from the associated forms in the comparatively smooth plates, 

 rounded base, regular curvilinear surface, and abruptly conical summit with few 

 plates. The third radials and second interradials are sometimes partially or entirely 

 obsolete or modified. 



Fig. 2 a. Anal side. 



Fig. 2 b. Anterior side, viewed against the left interbvachial space. 

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

 lington, Iowa. 



Actinocriiius forevicornis ( n. s.). 



PLATE X. FIG. 4 a, b. 



BODY urnshaped, depressed convex above and truncate 

 below, the sides much extended. Basal plates small, little 

 extended beyond the area of the column, which is slightly 

 depressed. First radial plates wider than long ; three hexa- 

 gonal and two heptagonal. Second radials slightly smaller, 

 and having the same proportions as the first ; four of them 

 hexagonal and one heptagonal. Third radials pentagonal, and 

 supporting on their upper oblique edges two brachial plates, 

 from which the arms proceed ; making five pairs from the 

 origin, each composed of a double series. Interradial plates 

 in three series of one, two, and three respectively. Anal 

 plates consisting of one in the first series ; three, four, four, 

 and six in the successive series ; above which, a series of 

 smaller plates surround the base of the proboscidiform aper- 

 ture which lies in the plane of the upper side of the brachial 

 openings. Summit depressed convex, composed of numerous 

 small plates arranged in systematic series ; the apicial plate 

 excentric posteriorly, prolonged into a short spine. The 

 sutures of the plates of the body below the arms are ca- 

 naliculate, giving relief to the individual plates. Surface 

 granulate or granulose-striate. Arms and column unknown. 



