HEXACEINID^. 771 



Basals large, occupying fully one tliird the height of the calyx, and form- 

 ing a rounded cup with obtuse angles upon the upper face ; the column facet 

 circular and slightly projecting. Eadials one quarter to one half longer than 

 wide, a little contracted at their lower ends, somewhat bulging at the middle 

 portions, and abruptly inflected at the upper ; facets less thau half the width 

 of the plates. Anal piece about the size of the radials, but narrower at the 

 top and more distinctly bulging. Costals two, small ; the first quadrangular, 

 twice as wide as long; the second a little larger and triangular, the upper 

 angle rather sharply pointed and bending inward, its sloping sides concave. 

 The line of union between the two costals, compared with those above and 

 below, quite obscure, constituting a syzygy, the epizygal joint supporting an 

 arm. A second syzygy unites the two proximal arm plates, with a pinnule 

 given off from the second. Arms two to the ray, twice or three times as 

 long as the calyx, comparatively stout, tapering to the tips, and biserial from 

 the third plate up. Arm plates of moderate length, with faces transversely 

 parallel; the two series united by a zigzag suture. Pinnules extremely long, 

 rather stout and closely packed ; they are composed of from ten to fourteen 

 joints, about three times as long as wide. Plates of the regular interradiiil 

 series three and two, all forming a part of the ventral disk. The anal side 

 has five plates in the lower range. Orals arranged in the usual way ; the 

 posterior one largest and pushed in between the other four. They form 

 a slight elevation, from which six well defined ridges pass out to the margin, 

 five of them ambulacra!, which divide and follow the arms ; the sixth con- 

 nects with the anus ; the ambulacral ridges are composed of two rows of 

 irregular pieces. The column in several perfect specimens averages eight 

 to nine inches in length ; it terminates in a fine point, and gives off at inter- 

 vals, one by one, short cirri. All stem joints, except close to the calyx, are 

 of equal length, and the older or nodal joints cannot be distinguished from 

 the intervening younger ones. Axial canal minute. 



Horizon and Locality. — Kinderhook group ; Le Grand, Marshall Co., 

 Iowa, where it is one of the most abundant species. 



Ti/pes in the collection of Wachsmuth and Springer. 



