178 PALAEONTOLOGY OF ILLINOIS. 



being but a single brachial piece to each division of the ray, 

 soldered into the walls of the body, and these rest directly 

 upon the third radials." What else could these plates be but 

 secondary radials? 



General form, without the arms, oblate-spheroidal, truncate 

 below. Dorsal cup in form of a basin which rests upon the basals 

 and portions of the first radials; wider than high, and spread- 

 ing but little at the sides. Plates moderately convex, without 

 ornamentation, suture lines well defined, with a small pit at 

 each angle of the plates. In color not distinguishable from D. 

 immaturus. 



Basals forming a very small disk, resting in a shallow con- 

 cavity, not visible in a side view. First radials large, hepta- 

 gonal, narrow below and wide above, so as to present an ob- 

 tusely triangular aspect; the upper corners truncate; upper 

 margins concave to receive the second radials. Second and third 

 radials small, of about equal size. Secondary radials 1x2x5, 

 succeeded in the three anterior rays by fixed brachials. In the 

 posterior ray to ward the anal side the secondary radial is axillary, 

 supporting two rows of arm plates, thus giving twelve arms to 

 the species. 



Arms biserial, with one or two cuneate joints succeeding the 

 radials, of which those of the same ray are laterally united. 

 The arms are proportionally more robust than in the two preced- 

 ing species, and resemble those of Agaricocrinus. 



Interradials in three ranges; the first very large, reaching to 

 the top of third radials. It supports two long, narrow plates, 

 which extend to near the arm-bases, and by still smaller plates 

 in the vault. First anal plate larger than the first radials, 

 hexagonal, higher than wide; the second anal, and the two in- 

 terradials on either side of it, about equal in size to the first 

 regular interradial. They are followed by about four ranges of 

 small plates, which lead to a circlet of very minute pieces, sur- 

 rounding a subcentral protuberance with a small lateral opening. 



Ventral side depressed, convex, summit plates nodose and 

 prominent; the central one large and projecting, in form of a 



