404 THE CEINOIDEA CAMEKATA OF NORTH AMEEICA, 



the upper one very short, leaf-like, and supporting the arms, except in the 

 two posterior rays, in which the distichal next to the anal side is axillary, 

 and supports on each side a single palmar, thus making the number of arms 

 in these rays three, against two in the three others. Arm facets very large, 

 directed oljliquely upwards. Ambulacral openings elongate, arranged in 

 groiiiDs, the interspaces between the rays twice as wide as those between 

 their subdivisions, and at the posterior side almost three times as wide, and 

 somewhat depressed. Structure of arms not known, but, to judge from the 

 size of the facets, they were unusually stout, and were biserial from their 

 origin. Interbrachials one, elongate, very large, arched by the arm-bearing 

 brachials. Anal plate longer than the radials, the lower angle sharp and 

 extending far down into the basal disk ; it is followed by three large plates, 

 and there is a smaller one between the palraars, which connects with the 

 interambulacral pieces above. A similar small plate occurs exceptionally 

 between the distichals at the other sides. Ventral disk depressed hemi- 

 spherical. The orals are i-aised into short spines or sharp nodes; the posterior 

 one central in position, a little larger, and less spinous. The radial dome 

 plates, which are fully as large as the orals, and are also extended into 

 spinous nodes, are placed around the periphery ; there is one of these plates 

 over the anterior and each antero-lateral ray, and three over the two poste- 

 rior ones ; the spines are directed slightly outward, and give to the tegmen 

 that peculiar coronate aspect which is so characteristic of this species. Inter- 

 ambulacral plates small, and merely convex. Anal tube subcentral, very 

 small at the base, its length not known. 



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



Type in the (Worthen) Illinois State collection. 



Eretmocrinus intermedius W. and Sp. 



Plate XXXIII. Figs. 2a, h, c. 



1881. W. and Sp. ; Revision Palajocr., Part II., p. 174. 



A small species. Dorsal cup broadly truncate at the bottom, the sides 

 straight or slightly convex. Plates almost flat ; the radial ones marked by 

 indistinct ridges, which pass into the arms ; the interradial plates covered 

 with a small central node, and all obscurely fluted toward their margins. 



Base short, broad, slightly jDrojecting laterally, rounded along the margin, 

 indistinctly grooved at the sutures, the lower surface excavated, and to one 



