50 



sloping sides two rather large plates tliat separate tbe seeoudary 

 and tertiary radials. These plates iu the second iuterradial range 

 unite with the plates of the vault and the sides of the projecting 

 radial series, but our specimen is loo mucii injured to follow far- 

 ther the order of arrangement. 



The first azygous plate is heptagonal, of the same size and in 

 line with the first primary radials. It is followed by three ratiier 

 large plates in the second range, that separate the second primary 

 radials, and, in turn, these are succeeded by a range of five some- 

 what smaller plates that separate the adjacent secondary and ter- 

 tiary radials. The third range, as thus indicated, is succeeded by 

 ranges of plates that cross the wide azygous area and form the 

 sides of the projecting radial series and thus unite with and be- 

 come part of the plates belonging to the vault. The graduation 

 from the plates of the calyx to those of the vault leave no definite 

 line of separation between them. 



The vault is convex and possessed of a balloon-like prominence 

 on the azygous side, part of which only is preserved iu our speci- 

 men, but it is certainly peculiar and distinct from that belonging 

 to any other described species. The opening appears to have been 

 seven or eight ranges of plates higher than the third range of 

 plates in the azygous area. All the radial areas are high, with 

 abruptly descending interradial ai-eas to correspond with the hori- 

 zontally projecting arms above described. Th(! plates of the vault 

 and balloon-shaped prominence are large, convex and polygonal, 

 with a smooth or finely granular surface. The plates dii'ectly over 

 the junction of the ambulacral passages bear spines and each one 

 over the junction of the ambulacral passages belonging to the five 

 radial series is particularly robust, though not of great length. 

 Our specimen is too much injured upon the vault for a minute 

 and careful definition of it, but the injury is mechanical ami what 

 we have is in a good state of preservation. 



This is a remarkable species, and (juite distinct from all hith- 

 erto described, though we think it is clearly referable to Dortjcri- 

 nus. 



Found by G. K. Gi'eene, iu whose honor we have proposed the 

 specific name, in what is called the Knobstone Group, at Button 

 Knobs, in Bullitt county, Kentucky, and which we suppose is the 

 age of the Keokuk Group. The specimen described is now in the 

 collection of AVm. F. E. Gurley. 



