542 GEOLOGICAL SURVEY OF IOWA. 



Platycriniis iiodobrachiatus ( n. s.). 



BODY small, abruptly spreading from the base, gibbous at 

 the sides ; base nearly flat, depression for the column mar- 

 gined by a thickened rim. Radial plateg gibbous in the mid- 

 dle ; articulating scar small. Subbrachial plates elongate, 

 somewhat pentagonal, thickened and slightly bilobed at the 

 upper extremity from which the arms bifurcate ; one of the 

 divisions again dichotomizing on the second plate above the 

 first : joints of the arms comparatively long, and thickened 

 at their upper extremities ; the upper alternating edges 

 projecting very prominently for the articulation of the ten- 

 tacula, giving the arms an apparent zigzag direction or no- 

 dosity at each joint. Tentacula composed of numerous joints, 

 which are also thickened at the articulating extremities. 



SURFACE granulose. Column small, composed of short al- 

 ternating thicker and thinner joints near the body, and, at a 

 greater distance, of elongated joints, which are thickened at 

 the articulations, and furnished with nodes or branchlets 

 just below each articulation. 



FIG. 63. 



^ji 



The accompanying diagram will illustrate 



the form of plates, character of arms, etc.; 

 the whole being enlarged two diameters. 

 There are about twenty joints visible in each 

 arm, fourteen of which are shown in the 

 figure; and on one of the arms, the tenta- 

 cula are shown extended. 



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

 lington, Iowa. 



