482 University of Kansas Geological Survey. 



five subradial ) present a stellate appearance, and form an area 

 not much greater in extent than the first radial plate. There 

 are three radial plates, varying in size and shape, either pen- 

 tagonal, hexagonal, or heptagonal. Of these three radial plates 

 the third or superior seems always the largest and most regular 

 in outline. It is heptagonal in form, with its two longest sides 

 sloping downward from the superior angle. The second radial 

 is about equal in size to the first. All are wider than high. 

 The third radial bears on its superior sloping sides in immedi- 

 ate succession five secondary radials, irregularly pentagonal, or 

 hexagonal in shape, and all wider than high. The fifth of 

 these approaches in shape the proximal armpiece, to which it 

 gives immediate support. 



" The arm pieces are thin and horizontally compressed from 

 without inward, their shape being subelliptical. The arms 

 give support to delicate pinnulse or tentacles throughout their 

 entire length. The articulate surfaces of the arm pieces present 

 a radiate structure. There is also on the inner side of each 

 arm piece a depression, the radial furrow, which gives to the 

 plates a subcrescentoid shape. The arm pieces decrease in size 

 toward the end of the arm. The interradial arms are irregular 

 in shape, somewhat contracted near the middle, becoming 

 wider above and below. They consist of about sixteen plates, 

 large, irregular, and varying widely in size, and of many 

 smaller ones, which gradually diminish in size to the apex, 

 forming a short arm. The arrangement of the interradial 

 plates varies, but in some specimens the order is as follows: 

 Commencing below, opposite the first radial, is a single plate ; 

 next above, in line with the second radial, are two ; and three 

 opposite the third. Succeeding these, and lying between the 

 first of the second radials, is a single, wide, octagonal plate, 

 and above this eight others, somewhat irregular, extending up 

 in pairs between the fifth secondary radials. Immediately 

 above these eight follow the smaller plates, diminishing rapidly 

 in size until the apex of the short interradial arm is reached. 

 A very small quadrangular plate is inserted between the first 



