PALEONTOLOGY OF IOWA. 633 



This species differs conspicuously from the preceding, both in the suhradial plates 

 and in the proportions of the radial plates, as well as in the number of plates in the 

 secondary series. 



FIG. 104. 

 a 





(V 



CWA The accompanying diagram illustrates the 



form and relations of the plates of the body, 

 and of two of the rays beyond the second sub- 



' dwsi - 



Geological formation and locality. In the Keokuk limestone : Warsaw, 

 Illinois. 



Forfoesiocriiius giddingei ( n. s.). 



PLATE XVII. FIG. 2 & 4. 



BODY subturbinate : rays prominent. Basal plates scarcely 

 projecting beyond the circumference of the column. Subradial 

 plates large, that of the anal side much longer than the 

 others ; those adjacent to the anterior ray truncated above 

 by the interradial plates. Radial plates more than twice as 

 wide as long, distinctly indented on their upper margin (and 

 the patelloid plate sometimes preserved ) ; the first ones 

 somewhat heptagonal ; the second and the third unequally 

 hexagonal, and the fourth pentagonal : plates of the second 

 division, three ; of the third division, four or five. Inter- 

 radial plates eight or ten. Anal plates numerous, undeter- 

 mined : interaxillary plate, one. Arms simple beyond the 

 third subdivision, giving to each ray eight arms, or forty 

 altogether (so far as determinable). Column round, composed 

 of thin joints, and rapidly tapering from its summit, Surface 

 finely granulose. 



SURVEY.] 80 



