578 GEOLOGICAL SURVEY OF IOWA. 



heptagonal and two hexagonal. Second radials octagonal, the 

 upper and lower sides horizontal and parallel. Third radials 

 pentagonal, supporting on their upper sloping sides the arm- 

 plates. First interradials hexagonal, supporting two plates in 

 the second range which are hexagonal or heptagonal, and lie 

 between the bases of the arms. Arms unknown, apparently 

 simple at base from each ray, and composed of a double series 

 of plates. Crown composed of numerous plates arranged in 

 somewhat regular series from the upper side of the arm- 

 bases : proboscis subcentral. The plates of the body below 

 the arms are marked by a strong angular ridge running from 

 each side, and meeting a similar one from the adjacent plate ; 

 the ridges meeting in a prominent node in the centre. Sur- 

 face of plates granuliferous. 



The specimen figured is remarkable for the absence of the first anal plate; the first 

 range of plates above the base consisting of only five, leaving the interradial spaces 

 essentially equal, as shown in the diagram. In another individual the first anal plate 

 is well developed, having the same size as the plates of the first radial series. 

 Fig. 6 a. Anterior side of specimen. Fig. 6 b. Posterior side of the same. 



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

 lington, Iowa. 



Actinocrinus verrucosus ( n. a.). 



PLATE X. FIG. 7 a, b. 



BODY urnshaped, with an extremely convex summit, ter- 

 minated by a proboscis : base deeply concave ; the outer 

 margins of the basal plates much extended in a broad thick- 

 ened rim, which is deeply notched at the junction of the 

 plates. First radial plates a little wider than long ; two 

 heptagonal and three hexagonal. Second radials hexagonal, 

 nearly twice as wide as long. Third radials pentagonal, or 

 sometimes with the upper lateral angles truncate, and sup^ 

 porting simple brachial plates which sustain the arm-plates 

 proper. Arms two from each ray at their origin, probably 

 subdividing above. First interradial plates hexagonal, sup* 



