PALAEONTOLOGY OF IOWA. 547 



Zeacrinus elegvms (n. s.). 



PLATE IX. FIG. 1 & 2. 



BODY subglobose, contracted above, concave below, the con- 

 cavity filled by the column. Basal plates minute, entirely hid- 

 den by the base of the column. Subradial plates six, projecting 

 rectangularly from the base and curving abruptly upwards ; 

 three pentagonal, two hexagonal, and one ( the anterior ) 

 quadrangular [ regarding the margins next the column as one 

 side], the latter placed between two pentagonal plates. First 

 radial plates five, wider than long : four of them pentago- 

 nal, being truncate above, with the sides nearly vertical, and 

 the sloping lower sides resting on two adjacent subradial 

 plates ; the anterior one hexagonal, being truncated below 

 by the quadrangular subradial. Second radial plates five ; 

 four pentagonal, and the anterior one quadrangular : anal 

 plates five. Arms dividing on the second radial of the pos- 

 tero-lateral and antero-lateral rays, while the quadrangular 

 second radial of the anterior ray supports a short pentagonal 

 third radial or brachial plate upon which the arm-plates 

 subdivide, each division again dichotomizing three times 

 before reaching the summit ; the branches coming off upon 

 the adjacent sides of the two arms from the same radial, 

 while those parts from the outer sides of the radials con- 

 tinue without branching on that side throughout their entire 

 length. Plates near the base of the arms unequally quadran- 

 gular ; those above, except the bifurcating plates which are 

 pentagonal, very short, quadrangular. Arms and branches 

 composed of a single series of plates : first bifurcations usu- 

 ally on the 6th, 8th, or 9th plate from base, varying in the 

 different rays. 



SURFACE finely granulose. Column round, apparently com- 

 posed of nearly equal thin plates. 



This beautiful species may be readily recognized by the peculiar arrangement of 

 its subradial plates; and should the quadrangular plate be only an individual and 



