PALEONTOLOGY OF IOWA. 585 



sloping sides a supraradial plate, which gives origin to two 

 simple brachial plates, whence the arms proceed, four from 

 each ray. First interradial plate heptagonal, smaller than 

 the first radial plate, and supporting two small hexagonal or 

 irregular plates ; and above these is a fourth, resting on the 

 inner oblique edges of the two below, and lying between 

 the bases of the arms. First anal plate as large as the first 

 radial : second anals as large as the first interradials ; these 

 support the third annl, which sustains the adjacent arm- 

 plates. Surface of plates marked by short angular ridges, 

 which terminate in a binodose transverse ridge on the first 

 radials, and in a strong angular node on the plates above. 

 Plates of the summit and proboscis somewhat tuberculous 

 or subspiniferous ; some of the latter sometimes raised in a 

 narrow transverse ridge, Arms and column unknown. 



Fig. 13. Anterior side of the specimen. 



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

 lington, Iowa, 



Actiiiocrinus coelatus ( n, s.) T 



PLATK X. FIG. 14 a, b. 



BODY short, subfusiform : base broadly truncate or slightly 

 concave ; summit teretely conical, and produced into a long 

 strong proboscis. Basal plates short, strong ; lower margins 

 much thickened ; sutures broadly grooved. First radial plates 

 broader than long, two heptagonal and three hexagonal ; the 

 right postero-lateral one as long as wide. Second radials once 

 and a half as wide as long, supporting on each upper oblique 

 side a hexagonal or heptagonal or rarely pentagonal supra- 

 radial plate : each of these sustain, on their upper oblique 

 sides, two other plates; the outer one (a brachial) sustains 

 on its truncated upper side a second brachial plate, succeeded 

 by a third, from which proceed the arm-plates. The inner 

 one is bevelled aboye, and supports on its outer sloping side 

 [ IOWA SURVEY.] 74 



