15 



two plates of the same size as the second primary radials or 

 first regular interradials, and each one bears a strong central 

 tubercle, with a radiating ridge directed toward each adjoining 

 plate. These are followed by three smaller plates, each of which 

 bears a central tubercle with radiating ridges toward the plates 

 below. These are followed by two small non-tuberculated plates, 

 which terminate the azygous area proper, though two or three 

 small, elongated plates separate the tertiary radials and connect 

 with the plates of the vault. 



This species has the general aspect of A. proboschlhilis. The 

 radial series, however, are more prominent and the interradial 

 and azygous areas larger, and each contains twice as many 

 plates. It is quite as far removed from A. dalyanus, in the 

 structure of the interradial areas, and in the surface ornamenta- 

 tion. 



It was found in the Drift, at Danville, Illinois, but no doubt 

 belongs to rocks of the age of the Burlington Group, imme- 

 diately north of Danville, and which are covered by the Drift. 

 The type is in the collection of Wm. F. E. Gurley. 



ACTINOCRTNUS ARROSUS, n. Sp. 



Plate II, Fig. 4, side view of a calyx, somewhat flattened. 



Specimen medium size. Calyx with a flanging base abruptly 

 truncated below, and rapidly expanding tertiary radials. Length 

 and breadth nearly equal; plates tumid and sculptured. Vault, 

 proboscis and arms unknown. 



Basals short, about half as high as wide, sharply flanged be- 

 low so as to make a broad, flat base with deep notches at the 

 basal sutures. The plates are longitudinally furrowed, so as to 

 further interrupt the flange and give it additional notches. 



First primary radials the larger plates of the body, as long 

 as wide, very tumid and protuberant, and having a small ridge 

 directed toward each adjoining plate. Second primary radials 

 about half as large as the first, nearly as long as wide, though 

 unequal in size and shape; two are quadrangular, two pentago- 

 nal and one hexagonal; they are tumid and have a small ridge 

 directed toward each adjoining plate. Third primary radials of 

 unequal size and shape, some larger than the second radials and 



