20 



radials, the second one of which is axillary and bears upon each 

 superior side one tertiary radial. The arms then bifurcate on the 

 third plate, which gives to this ray six arms. It will be noticed 

 that these rays are quite different and yet result in producing 

 the same number of arms. The lateral rajs, as far as they can 

 be seen, on our specimen, appear to be constructed in the same 

 manner as the two above described. The ray opposite the azygous 

 side may have the same number of arms and it may have two 

 less. We can see seventeen arms, the others are covered. The 

 species, therefore, as near as can be ascertained has either twenty- 

 eight or thirty arms. The arm* are large, long, and composed of 

 a double series of small interlocking plates, that bear long pin- 

 nules. 



The regular interradial area on the left of the azygous side is 

 elongated, extends to the vault and contains five plates. The first 

 is medium size and rents between the superior sloping sides of 

 two first primary radials; it is followed by two somewhat smaller 

 plates in the second range, and these by one of about the same 

 size in the third range, and this by an elongated plate in the 

 fourth range, that separates the arm-bearing plates of the calyx 

 and unites with the plates of the vault. No other regular area 

 can be described from our specimen. The azygous area is elongate, 

 subovate and contains nine or more plates. The first plate is in 

 line with the first primary radials and quite as large. It is fol- 

 lowed by three plates in the second range, and these by three in 

 the third range, and these by two plates in the fourth range that 

 separate the arm-bearing plates, and one of which unites with the 

 plates of the vault. 



This species will be distinguished by its smooth calyx, slightly 

 lobed by the projecting radial series at the summit of the calyx, 

 and depressed interradials, that separate the arm-bearing plates; 

 by the shape of the regular and azygous areas and the numbar of 

 plates which they contain, and their connection with the plates of 

 the vault, which is so exceedingly rare in this genus; and by the 

 structure of the radial series and number of arms. We know of 

 no species with which it is necessary to make a comparison, or 

 for which it might be mistaken. 



Found by Mr. N. K. Burket, in the Keokuk Group, at Hamilton, 

 Illinois, and now in the collection of Wm. F. E. Gurley. 



