GEOLOGICAL SURVEY OF IOWA. 



not a specific character, the body and base of arms, as well as their mode of dicho- 

 tomizing, is peculiar. 



Fig. 1. Anterior side of specimen. 



Fig. 2. Posterior side, showing the anal plates. 



Fio. 



The accompanying diagram (fig. 68) illus- 

 trates the form and arrangement of the plates 

 in the subradial and radial Series ; as also of 

 the arms of the second bifurcation or first 

 above the radial, showing the supernumerary 

 plate in the anterior ray. 



Geological formation and locality. In the Burlington limestone 

 lington, Iowa. 



Bur- 



Zeacriiras ramosus (n.s.). 



PLATE IX. FIG. 3. 



Bot)Y small, cupform, concave below, with arms spreading. 

 Basal plates unknown. Subradial plates concave towards the 

 column, becoming thickened and gibbous in the middle and 

 towards the upper margin. First radials short, pentagonal, 

 the two sides resting upon the sloping edges of two adjacent 

 subradial plates. Second radials a little longer than the first, 

 pentagonal, the anterior one quadrangular. Arms resting on 

 the pentagonal radials, double from their origin, and bifur- 

 cating again on the sixth plate above ; and again bifurcating 

 twice, with eight or nine plates intervening between each, 

 the bifurcations coming off on the inner adjacent sides of the 

 two divisions from the same ray. Arm from the quadrangular 

 anterior second radial simple to the fourth joint, where it 

 dichotomizes ; each branch again dichotomizing upon the 

 eighth and tenth joint respectively above. Arm-joints in 



