53 



still smaller, much wider than long, hexagonal, axillary, and 

 bears upon each superior side a single secondary plate, which 

 is short and axillary and bears tertiary radials, which gives to 

 this ray four arm openings to the vault. In the radial series, 

 on the left of the azygous area, the first primary radial is 

 small, longer than wide, pentagonal, and followed by a second 

 primary radial, nearly as large, longer than wide, hexagonal, 

 and followed by a third primary radial, much wider than long, 

 octagonal, axillary, and bearing on the superior sloping sides 

 a single secondary radial, which is axillary and bears tertiary 

 radials, which gives to this ray four arm openings to the 

 vault. It will be observed that the three radial series that 

 truncate the basal disc have, each, three primary radials, 

 though the plates differ in relative form and size There are, 

 therefore, nineteen arm openings to the vault. The first arm 

 plates are small, and the arms are directed horizontally. 

 Beyond this, the arms are unknown. 



The interradial areas differ, in form, and in the number of 

 plates, and in position, as much as the radial series do, and, 

 though they all connect with the vault and the plates grow 

 less in size, until they unite with the plates of the vault, they 

 will be separately described. In the area on the right of 

 the azygous area, the first plate rests on the basal disc. It is 

 large, longer than wide, hexagonal and is followed by two 

 rather large plates in the second range, and five in the third 

 range, which connect with the plates of the vault, but in this 

 species there is no line separating the plates, in the inter- 

 radial areas, from the vault, as they all graduate into each 

 other. In the area on the left of the azygous area, the first 

 plate rests on the basal disc. It is large, much longer than 

 wide, heptagonal, and is followed by two plates, in the second 

 range, that unite with three plates which belong to the vault. 

 In the area on the right of the radial series that truncates the 

 pentagonal plate belonging to the basal disc, the first inter- 

 radial rests between the superior lateral sides of the first 

 primary radials. It is moderately large, hexagonal, and is 

 followed by two plates in the second range that unite with 

 three plates belonging to the vault. In the area on the left 

 of the radial series that truncates the pentagonal plate be- 



