PALAEONTOLOGY OF IOWA. 587 



Fig. 14 a. Left postero-lateral side, partially showing the anal side ( the specimen 

 slightly distorted ) . 



Fig. 14 b. Antero -lateral view of same specimen. 



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

 lington, Iowa. 



Actinocrinus tnrbinatus (n.s.). 



PLATE XI. FIG. 1. 



BODY symmetrically uniform : calyx with sides straight 

 or very slightly concave, in a line from the basal to the 

 brachial plates ; the dome curving regularly upwards to the 

 base of a strong proboscis : base abruptly concave, for the 

 reception of the column. Basal plates thick, short, forming 

 a distinct rim projecting over the column. First radial plates 

 proportionally very large, about once and a half as wide as 

 long. Second radials very small, quadrangular. Third radials 

 small, pentagonal, supporting on each of the upper oblique 

 faces a series of two supraradials, which again divide on the 

 second plate above, giving origin to four brachial plates in 

 the anterior and antero-lateral rays ; while in the postero- 

 lateral rays there is a third supraradial plate intervening on 

 the anal side, giving origin to an additional arm from each 

 of those rays. This gives five arms to each postero-lateral 

 ray, and four arms to each 



4 



of the other rays = 4 4 22 arms. 

 ~5~ ~5~ 



First interradial plate ten-sided, resting on adjacent radials 

 below, and flanked on either side by the second and third 

 radials and first supraradials, and above by the second range 

 of interradials, one or two in number, which support a small 

 single hexagonal interradial in the third series. First anal 

 plate larger than the first radials, as wide as long, supporting 

 three anal plates in the second range, the central one of 

 which is hexagonal and the two outer ones heptagonal : third 



