592 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



little beyond the sides of the column ; column facet concave. Eadials once 

 and a half as wide as long, the sides rapidly spreading. First costals fully as 

 wide as the radials, but considerably shorter, subquadrangular in outline, but 

 generally hexangular. Second costals a little longer than the first, and 

 directed slightly downward, as also the distichals. Distichals nearly as large 

 as the second costals, and all axillary, supporting upon each side two moder- 

 ately large palmars, which are laterally connected and support the free arms, 

 of which there are four to the ray. Arms simple, long, heavy, rounded in 

 the lower portions, flattened and wider in the upper; the tips incurving. 

 The two proximal arm plates cuneate, the two rows of ossicles succeeding 

 them moderately long, and every sixth one extended into a sharp lateral 

 spine. The spines increase in length upwards, commencing as small nodes, 

 and attaining at the upper part of the arms a length of 2 or 3 mm., the cor- 

 responding ones placed opposite. First interbrachial comparatively small, 

 higher than wide, followed by two rather large j)lates in the second row, and 

 one or two smaller interambulacral pieces at each side. Anal plate remark- 

 ably small, only half as wide as the radials, supporting two plates, which are 

 followed by three large and two smaller ones at the sides, the latter bending 

 oi;tward, helping to form the free rays. Plates of the ventral disk slightly 

 convex, their surface covered with small pustules without definite arrange- 

 ment. Orals a little larger than the other plates, and formed into short 

 spines ; the posterior one placed at the side of the anal tube. Anal tube 

 excentric and very short, directed obliquely u]oward. No ambulacral plates 

 are visible to the base of the free rays, where those of the first and second 

 order are represented by single plates. Column composed of rather long 

 joints ; the nodal ones considerably widest and rounded along the margin ; 

 the axial canal small and pentagonal. 



Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa, 

 and Lake Valley, New Mexico. 



Remarks. — This species is readily distinguished from all others by its 

 arm structure. 



Tiji^e in the (Worthen) Illinois State collection at Springfield. 



