610 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Basals forming a shallow cup, the sides gradually expanding but not 

 thickened; the upper margins distinctly angular. Eadials large, fully as 

 long as wide. Costals one half smaller, almost as wide as long. Palmars 

 quite small, the two inner ones of each ray giving oft' two arms, the outer 

 ones but one. Arm bases a little projecting, the facets moderately large and 

 concave; arm openings arranged in groups, those of adjoining rays twice 

 as far apart as those within the ray. Eespiratory pores slit-like. Structure 

 of the arms unknown. Regular interbrachials : 1, 2, 2, 1, succeeded by a 

 small elongate piece, wedged in between the arm-bearing brachials; the 

 first as large as the costals, those of the second row equal in size to the 

 distichals. The anal plate, which is as wide at the bottom as near the top, 

 is followed by 2, 3, 2, and 2 plates, the latter generally suiDporting two small 

 elongate pieces, which are in contact with the interambulacrals. The 

 interdistichal spaces are deeply depressed, and occupied by a single flat 

 piece. Ventral disk subconical, gradually passing into the anal tube, which 

 is almost central, and very stout. The disk, as well as the tube, is composed 

 of an immense number of all sorts of plates ; some of them are large and 

 take the form of elongate nodes or small spines, others are smaller and have 

 rounded nodes; while the smallest ones, which are interspersed profusely 

 between the larger, are simply convex. Orals extremely excentric, small, 

 and separated by small plates ; the posterior one, which .stands erect and 

 bears a transverse node, takes part in the tube. Radial dome plates sub- 

 spinous, irregularly arranged, and placed at some distance from the arm 

 bases. 



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



Type in the Museum of Comparative Zoology. 



BemarJcs. — Meek and Worthen's figure in the Illinois Report is some- 

 what misleading ; the plates of this species are generally less convex, the 

 suture lines almost obsolete, and the radiating ridges upon the plates more 

 distinct than shown in that figure. 



