18 



The regular interradial areas are elongated, unequal, and con- 

 nected with the vault. In one area there are two plates, one, 

 followed by an elongated plate that connects with the vault. In 

 another area there are four plates, one, followed by two plates in 

 the second range, and an elongated plate that connects with the 

 vault, in the third range. In each of the other two areas there 

 are three plates, one, followed by two in the second range, that 

 connect with the plates of the vault. The interradial areas are 

 depressed below the radials, which gives the subpentagonal out- 

 line to the body. The azygous area is nearly perpendicular from 

 the constriction of the basals to the orifice, with a central longi- 

 tudinal, convex ridge. The first azygous plate is in line with the 

 first primary radials, larger than either one of them, and bears a 

 transverse central node. It is followed, in the second range, by 

 three plates, the middle one being the largest and most convex. 

 The middle one is followed by two large nodose plates, the last 

 one of which abuts upon the azygous orifice. The plates upon 

 each side of the longitudinal central ridge, formed by these no- 

 dose plates above the second range, are small and depressed. On 

 one side, below the plates surrounding the orifice, there are three 

 plates and on the other four. The azygous orifice is surrounded 

 by five plates and is situated below the level of the horizontally 

 extended spines belonging to the vault. 



The vault is elevated above the ambulacral openings so that a 

 transverse section is subpentagonal, but it is stellate, as seen from 

 above, by reason of a very large plate above each radial series' 

 terminating in a large spine, directed horizontally. In each of the 

 lateral rays a large elongated plate separates the small ambulacra] 

 openings and extends to the inferior side of the spinous plate 

 In the other rays an elongated plate occupies the same position, 

 and laterally there are two plates extending to the spinous plate, 

 the lower ones separating the ambulacral openings. The vault is 

 nearly flat on the top, where it is covered by a few convex plates 

 and a lai'ge central spinous plate. There are, therefore, six plates 

 that terminate in spines, one central and directed upward and one 

 over each radial series directed horizontally. Each spine is ab- 

 ruptly contracted or constricted, in the middle part, and then 

 extends without tapering until it approaches the point. The point 

 is broken off from each of the spines, in our specimen, but one 

 of them is evidently nearly complete, as shown in the illustration. 



