26 



upper sloping side two secondary radials, the last of which is 

 axillary and supjiorts upon each upper side two tertiary 

 radials which gives to each of these rays four arms. Upon 

 the distal side of the third primary radials adjoining the azy- 

 gous area there are four secondary radials, and on the proxi- 

 mal side two secondary radials, the last of which is axillary 

 and bears upon the distal side two tertiary radials, and ujjon 

 the proximal side three tertiary radials which arrangement 

 gives to each of these rays three arms. In the ray opposite 

 the azygous area there are three secondary radials upon each 

 side of the third x'rimary which gives to this ray two arms. 

 There are, therefore, sixteen ambulacral openings to the vault 

 in this species, and the last radials are small and contracted 

 which makes it probable that the arms, which are not pre- 

 served, are single and not large. 



There are three regular interradials in each area, one fol- 

 lowed by two in the second range that are short and enclosed 

 below the tertiary radials so that they do not approach the 

 vault. The first azygous plate is in line with the first i)rimary 

 radials and somewhat longer, and it is followed, in the second 

 range, by four plates that very much widen the lower part of 

 the area. There are four plates in the third range and these 

 are followed by a single narrow elongated plate thr.t connects 

 with the plates of the vault. 



The vault is low and has about the same caiiacity as the 

 calyx. It is covered with polygonal, convex plates and bears 

 a small subcentral proboscis. The ovarian apertures are con- 

 spicuous in this species. There are two between each pair of 

 arms and one between the secondary and tertiary series in the 

 three-armed .rays, which makes sixteen in the species. They 

 ai-e above the calyx and connect with tlic ambulacral canals 

 under the vault. 



This species is distinguished by its general form, sixteen 

 arms, four azygous plates in the .second range, short regular 

 inten-adial areas, and ovarian apertures. It cannot he mis- 

 taken for any other desc^rlljcnl species. 



Pound by S. A. Miller in the Keokuk Groui». at Boonville, 

 Missouri, and now In his cjllect'on. 



