350 PALAEONTOLOGY OF ILLINOIS. 



jecting downward a little around the column, in the form 

 of little nodes, formed by deep notches at the sutures and 

 smaller ones between. First radials generally wider than 

 long. Second radial pieces somewhat smaller than the 

 first, wider than long, some hexagonal and others pentago- 

 nal. Third radials a little smaller than the second, gener- 

 ally pentagonal and bearing on each superior sloping side a 

 secondary radial, each of which supports one or more bra- 

 chial pieces, leading to an arm on its outer sloping side, and 

 a small tertiary radial on its inner, each of which evidently 

 supported two other pieces above, one or both of which 

 were probably brachials. If both sides bore brachials it 

 would make six arms to the ray, but if one side bore an 

 auxiliary piece it would make eight to the ray, or forty to 

 the whole series. 



First anal piece of about the same size as the smaller first 

 radials, slightly longer than wide, hexagonal in form, and 

 succeeded by two smaller hexagonal or heptagonal pieces 

 in the second range, above which there seems to be about 

 four other smaller pieces. Subradials three or four to an 

 area, the first one about as large as the second radials, hex- 

 agonal or heptagonal in form, and supporting two smaller 

 pieces in the next range ; above this there seems to be one, 

 or possibly sometimes two other smaller pieces. Auxiliary 

 spaces sometimes occupied by one or two small pieces. 



Yault much depressed, or rising little above the horizon 

 of the arms, composed of irregular small and moderate 

 sized pieces, and provided with a nearly central proboscis, 

 which in the typical specimen is composed of very small 

 pieces at the base, and a little inclined to one side. 



Surface of body plates all prominent and angular in the 

 middle, and provided with well defined, sharp radiating 

 costse, which are compound on the first radial and first anal 

 pieces, but generally consist of a single rib, extending from 

 the middle to each of the sides of the others. The mesial 



