BATOCRINID^. 457 



costals, the arm regions distinctly lobed, the interradial spaces shghtly flat- 

 tened below and deeply depressed above. Plates formed into high nodes, 

 which on the radials and brachials are transversely arranged and sharply 

 angular, but on all interradial plates are circular and pointed. 



Basal cup large, distinctly trilobate, three times as wide as high, the 

 lower margins projecting, broadly notched along the sutures, the bottom 

 deej)ly excavated for the reception of the column. Radials once and a half 

 as wide as long, rapidly spreading to two thirds their height, the upper face 

 concave. First costals half the size of the radials and quadrangular ; the 

 second generally heptangular, sometimes pentangular or hexangular, owing 

 to the height of the first interbrachials. Distichals one, axillary, narrower 

 than the costals, giving off from each side an elongate palmar ; except in 

 the antero-lateral rays, in which only the side of the costal toward the 

 anterior ray bears an axillary, the other side two distichals, of which the 

 second is twice as long as the first. The distichals and palmars have much 

 the appearance of arm plates, being rounded exteriorly, so as to form a 

 deep groove at each side. Arms arranged in groups, with wide and deep 

 depressions between the rays. When normally developed, there are eigh- 

 teen pairs : t^, but most of the specimens have a few single ai'ms irre- 

 gularly scattered between the paired ones. Arms thin and short, rounded 

 on the back throughout their full length, their tips slightly tapering. First 

 interbrachial large, generally longer than wide, its central part extended 

 into a conspicuous node ; the two of the second row about one half smaller ; 

 the plates of the third smaller still, followed by larger plates in the ventral 

 disk. Anal interradius very wide, flat, and exceedingly deep at the arm 

 regions ; it consists of a longitudinal row of four large elongate anal plates, 

 with smaller pieces above, forming a protuberance and enclosing the anal 

 aperture. At each side of the second anal there is a large interbrachial, 

 succeeded by several smaller ones on a level with the third anal. Ventral 

 disk similar to that of D. mismsippiemis, and the plates arranged in the 

 same way ; the spines, however, are somewhat longer, less tapering, and 

 in the larger specimens are covered at intervals along the upper portions 

 by small spiniferous nodes. The secondary radial dome plates, and the 

 interambulacral between them, are somewhat smaller than in that species, 

 and hence the height of the disk is a little less. Anal opening on a level 

 with the lateral spines; facing laterally. 



Horizon and Locality. — Middle part of the Keoknk group. Eare at 



38 



