34 



angle on the azygous side, so as to make it pentagonal; and it is 

 then followed by a fourth primary radial which is pentagonal and 

 axillary, and bears upon the upper sloping side the secondary radi- 

 als or free arms. The arms preserved in our specimen have three 

 short, secondary radials, in each, the last one of which is pentag- 

 onal and supports, on each upper sloping side, a third series of 

 plates. 



There are two small regular interradials in each area, one above 

 the other; the first one separates the second and third primary 

 radials, in each series, in some of the areas, it truncates the su- 

 perior angles of the first primary radials, in others it does not ex- 

 tend so low. The first azygous plate is rather larger than the first 

 primary radial on the right and has eight sides; it truncates a sub- 

 radial, abuts upon three primary radials on the right, though the 

 third one truncates the angle only slightly, two on the left, and 

 is followed by two plates on the superior side, the one on the left 

 being quite small. The larger plate in the second range is suc- 

 ceeded by a small plate on the right, which is all that is preserved 

 in our specimen, but the facet for another plate in the middle part 

 is well preserved. The azygous area, therefore, has five or more 

 plates. 



This species is readily distinguished from all others by the gen- 

 eral form, regular interradial plates, azygous interradials and series 

 of four primary radials in one of the rays. It is wholly unneces- 

 sary to compare it with any of them, though it clearly belongs to 

 this genus. 



Found in the Niagara Group, at Oswego, Illinois, and now in 

 the collection of Wm. F. E. Gurley. 



