198 PALEONTOLOGY OF ILLINOIS. 



are axillary, are sharply angular at their upper faces, and pro- 

 vided with two articular facets and two impressions for the 

 reception of patelloid plates. Secondary radials three; by one- 

 half narrower than the preceding ones, and somewhat shorter, 

 but not in proportion to the decrease in width, except the 

 axillary one, which is comparatively shorter and also wider. 



The next order of plates consists variously of from 3 to 5 or 

 6 pieces, with another bifurcation above. These plates are all 

 arranged on the plan of the primary radials, like them they are 

 flat at their outer sides, and united in a similar manner as 

 those, which makes it difficult to ascertain the actual com- 

 mencement of the arms. This difficulty is increased by the 

 fact that the rays are free from the top of the primary 

 radials, while their main divisions remain united all along the 

 secondary radials by means of interaxillary plates. Perhaps 

 these rays formed a kind of free appendage like those of the 

 Platycrinidse and Hexacrinidse, a question, however, which can- 

 not be solved unless we find the ventral covering intact. 



Interradials three; elongate; the two upper ones much smaller, 

 extending to the top of the primary radials. There are gener- 

 ally three somewhat smaller interaxillaries, arranged longitu- 

 dinally, which unite the secondary radials. Smaller specimens 

 have but one or two. The azygous side is composed of a row 

 of from 3 to 4 or more tube-like anal plates, longitudinally ar- 

 ranged, which rest upon the truncate upper face of the poster- 

 ior basal. There are no traces of interradials to connect these 

 plates with the radials. 



Column extremely stout, almost large enough to support a 

 species of twice the size of this. It is inflated near the calyx, 

 and, along the upper part for about an inch, is composed of 

 rather short, very uniform joints, w r hen suddenly the aspect of 

 the column changes entirely, the joints, at their margins, 

 become more convex, and larger and smaller joints alternate 

 with one another, the larger ones extending conspicuously be- 

 yond the smaller ones. 



Geological position, etc. : The same as that of the last species. 



Our own collection. 



