51 



nearly parallel. Third primary radials rather longer and wider 

 than the second, pentagonal, axillary and bear upon each supe- 

 rior sloping side a single secondary radial. The secondary radials 

 are of unequal size, part heptagonal and part hexagonal, and bear 

 upon each superior sloping side four tertiary radials. The first 

 tertiary radials are moderately large, the others are quite short. 

 There are, therefore, twenty arms and twenty ambulacral openings 

 to the vault in this species. There are no intersecondary or inter- 

 tertiary plates. 



The first interradials are very large plates and have nine sides. 

 They are followed in the second range, by a single plate, which 

 is about half or less than half the size of the first. In some of 

 the areas, there are two plates and in others three plates, in the 

 third range, that connect with the plates of the vault. The azy- 

 gous area is wider than either of the regular areas and the first 

 plate is the largest in the calyx and has eleven sides. The addi- 

 tional sides are produced by abutting against the first tertiary rad- 

 ials, which the first plate in the regular areas does not reach. It 

 is followed in the second range by a single plate larger than the 

 second plate in the regular areas. There are three plates in the 

 third range that unite with the plates of the vault. 



The vault is moderately convex over the ambulacral areas and 

 depressed in the interradial areas, most depressed in the azygous 

 area. Most of the sutures between the plates of the vault are 

 destroyed, in our specimen, but where the plates can be distin- 

 guished, they are large. The proboscis seems to be complete, in 

 our specimen, and, as may be seen in the illustrations, the plates 

 are merely elevated around a subcentral azygous opening. There 

 is a minute orifice on each side of each arm base, which we sup- 

 pose represent the ovarian apertures, but they are so small for so 

 large a specimen that we suppose the silicification has partly 

 closed them. They are not down in the interradial areas, as in 

 other species, but are differently located. 



The general form, surface ornamentation, interradial and azy- 

 gous areas and twenty arms will readily distinguish this species 

 from all others that have been described. It is a marked and 

 beautiful species. 



Found in the Hamilton Group, at Charlestown, Indiana, and 

 now in the collection of Wm. F. E. Gurley. 



