PALEONTOLOGY OF IOWA. 589 



These differences, though affecting the structure of the body in a degree, do not 

 appear to me of specific importance, unless other specimens should show a constancy 

 in these characters. 



Fig. 5. View of the anterior side. 



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

 lington, Iowa. 



Actinocrinus longirostris ( n. s.). 



PLATE XI. FIG. 2, 2 a, b = ( 4 c, 4 d ) . 



BODY symmetrically uniform, with convex sides : summit 

 regularly convex to the base of a strong elongated proboscis. 

 Basal plates turgid, moderately concave at the base for the 

 reception of the column, and marked by broad shallow 

 grooves along the suture lines. First radial plates tumid, 

 large, wider than long ; two very distinctly heptagonal, and 

 three hexagonal. Second radials small, quadrangular (one 

 sometimes irregularly pentagonal). Third radials hexagonal, 

 with the lateral margins short, the upper oblique edges sup- 

 porting each two supraradial plates, the highest of which is 

 pentagonal, and upon the upper oblique faces supports the 

 brachial or subbrachial plates from which proceed the arm- 

 plates of two arms, making four arms from each ray except 

 the anterior ray. The last radial plate supports on each side 

 two brachial plates in succession, giving one pair of arms to 

 this ray ; making two from the anterior, and four from each 

 of the other rays ; 



2 



making the number == 4 4 = 18 arms. 

 T T 



First interradial plate large, hexagonal, supporting on its 

 upper sides two second interradials, and sustained laterally 

 by the second and third radials. Third interradials supporting 

 an elongate plate which lies between the bases of the arms. 

 First anal plate a little larger than the first radials, supporting 

 three in the second range ; the central one hexagonal, and 



