582 GEOLOGICAL SURVEY OF IOWA. 



FIG. 85. 



A 



/;\>,- 5 The accompanying diagram ( fig. 85 ) 



B^^C^ consists of the anterior and right antero- 



i %>^ & ^P^ lateral rays of this species, illustrating the 



[ISagx 'W? 5 , r\ /^?r?Cv structure of the ray in its supraradial and 



(P(g}rg) <>W>. ^ -1 /-*$> \-3r\rf>\ 



s^Si) ^CD ^T) CV brachial plates and the mode of origin of 



i^(*$$3\^\^Ej/\C$^Q' O3 ^ e arms > each terminal plate, as repre- 

 ^ vfx%<EVO ^ ^ sen ted, being the base of an arm as shown. 



The same diagram also illustrates the 

 structure of the anterior and left antero- 

 lateral ray as far as the bases of the arms, while the right antero-lateral ray shows 

 the plates of the arms above the brachial plates. 



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

 lington, Iowa. 



Actinocrinus sculptus ( n. s.). 



PLATE X. FIG. 11 a, b. 



CALYX broadly turbinate : base truncate, and slightly 

 depressed in the centre. Basal plates moderately large, the 

 two larger twice as wide as long. First radial plates about as 

 wide as long ; the anterior plates the longest, and the two 

 postero-lateral ones distinctly smaller. Second radials much 

 smaller, hexagonal. Third radials hexagonal, thickened on 

 the upper edge, and supporting an irregular brachial plate 

 upon which the arm-plates are subdivided, giving origin to 

 three arms from each ray, the central one of which may 

 perhaps be again subdivided, making fifteen or perhaps 

 twenty arms altogether. First interradial plate as large as 

 the second radial, supporting two smaller interradials, and 

 these a third series of three or four which lie in a range with 

 the first arm-plate. First anal plate nearly as large as the 

 first radial ; and the second range, consisting of two plates 

 of the same size as the second radials : third anal range, 

 three plates ; fourth, five ; and the fifth series six or seven 

 plates, lying in a direct horizontal range between the bases 

 of the arms. 



SURFACE of plates marked by abrupt narrow ridges in 



