25 



area, there are two secondary radials, and on the proximal 

 side a single secondary radial, which is axillary and supports 

 upon the distal superior sloping side a single tertiary radial, 

 and on the proximal side two tertiary radials which gives to 

 each of these rays three arms. There are, therefore, in this 

 species twelve arms. The last tertiary and secondary radial in 

 each series is thicker and more convex than the adjoining 

 plates, and the ambulacral openings are in part exposed in a 

 basal view. 



In one of the regular interradial areas there are only two 

 plates, in eacn of the other three regular interradial areas 

 there are three plates. The first one rests between the super- 

 ior sloping sides of the first primary radials and extends up 

 between the first secondary radials. It is followed by one nar- 

 row elongated plate in one of the areas and by two narrow 

 elongated plates in the other areas that connect with two plates 

 belonging to the vault. The first azygous plate is in line with 

 the first primary radials, about as large and heptagonal. It is 

 followed by three plates in the second range, which are sub- 

 equal in size, and each wider than long. In the third range 

 there is a single plate that separates the tertiary radials and 

 extends to the top of the calyx, where it is truncated the full 

 width and unites with a single plate belonging to the vault. 



The vault is moderately convex and is covered with large, 

 convex, polygonal plates and a very large heptagonal central 

 plate that supports a long, robust, conical spine. The spine 

 commences to rise at the sutures of the seven adjoining plates. 

 There is no indication of an azygous orifice, but the sutures 

 between some of the plates on the azygous side of the central 

 spine are obscure and possibly the orfice was covered with valvular 

 plates, which have fallen back in place so as to absolutely 

 close it without preserving the sutures. But in any event the 

 orifice must have been very small. 



This is a peculiar species, probably more nearly related to 

 .4. hodgsoui than to any other heretofore described. It does not 

 need any comparison, however, with that species to distinguish 

 it. 



Found by C. S. Hodgson in the Burlington Group, in Adams 



county, Illinois, and now in the collection of S. A. Miller. 

 —4 



