19 



the first radials, while they curve upward vertically from near or 

 below the middle; each supporting on the upper side a much smaller 

 hexas^onal piece, which rises vertically, and usually bears on its 

 short superior lateral edges two smaller pieces connecting with 

 the secondary radials or first arm-pieces, while its short truncated 

 upper side is not surmounted by any succeeding piece, but con- 

 nects on its inner surface with the vault. 



"Sutures between all the plates channeled. Surface of body 

 plates ornamented with raised lines or very small radiating costa?, 

 that cross the sutures parallel to each other at the sides of the 

 plates, but soon become bent about and connected, in various 

 ways, so that very few of them extend directly to the middle of 

 any of the plates, the arrangement being such as to produce a 

 kind of vermicular style of ornamentation, especially over all the 

 central part of the plates, like that often seen on the body plates 

 in ADijjhorncriuKS. A small rather sharp ridge also extends up 

 the middle of each radial series of plates, more or less interrupted 

 at the sutures, and showing a slight tendency to form a pinched 

 node on the middle of the first and second radials; while it is 

 sometimes seen to bifurcate on the third radial, to send branches 

 to the secondary radials, but these are generally so small as 

 scarcely to be distinguished from the other little ridges ornament- 

 ing all of the body pieces. 



"Ventral tube unknown, but judging from the spiniferous char- 

 acter of the vault-pieces around its base, probably also spiniferous. 

 "Height of body to arm-bases, 0.47 inch. do. to top of vault, 

 0.60 inch; breadth, 0.95 inch." 



The specimen illustrated is from the typical locality, in the 

 Upper Helderburg Group, at Columbus, Ohio, and is from the col- 

 lection of Charles Faber. It will be observed that it is about the size 

 of the type described by Meek, and agrees with it ia all particulars. 

 The variety asperaius, above described, has a proportionally longer 

 calyx, which produces some difference in the relative sizes of the 

 plates, but this aloue would not be of varietal importance; taken, 

 however, in connection with the different surface ornamentation 

 and the great difference in the ridges that cross the radial plates, 

 varietal characters may exist. The plates on the superior lateral 

 sides of the second interradials are proportionally smaller in 

 D. ornaius than in D. ornalus iiar. aspevatus and other minor 

 differences might be pointed out, but they do not seem to us to 



