28 



and those abutting on two basals heptagonal. They are not 

 visible in a side view. The second primary radials are as 

 large as the first, hexagonal, and differ considerably in size. 

 The third primary radials are also unequal in size, as large 

 as the first or second, three heptagonal, two hexagonal, axillary, 

 and, in the ray on each side of the azygous area and in the 

 ray opposite the azygous area, bear on each upper sloping 

 side a single secondary radial, which is axillary, and supports 

 on each upper sloping side two tertiary radials, which gives 

 to each of these rays four arms. In one of the lateral rays 

 the third primary radial bears upon each upper sloping side 

 three secondary radials, which gives to it two arms. In the other 

 lateral ray, the third primary radial supports, on one superior 

 sloping side, three secondary radials, and on the other a single 

 secondary radial, which is axillary and supports on each upper 

 sloping side two tertiary radials, which gives to it three arms. 

 There are, therefore, seventeen arms and seventeen ambulacral 

 openings to the vault in this species. 



In each regular interradial area there are eight plates, the 

 first one is hexagonal, rests between the upper sloping sides 

 of the first primary radials, separates the second primary ra- 

 dials and is followed by two plates nearly as large in the sec- 

 ond range, three in the third range and two in the fourth 

 ronge, that separate the arms and unite with the plates of the 

 vault. There is one plate in each of the intersecondary radial 

 areas that connects with the vault, except in the two-armed 

 lateral ray where the secondary radials unite. The azygous 

 area is large and contains tw T enty-one plates. The first one is 

 in line w T ith the first primary radials and of the same size, it 

 is followed by three somewhat smaller plates, in the second 

 range, five plates, in the third range, five plates, in the fourth 

 range, four plates, in the fifth range, and three plates, as near 

 as can be determined, in the sixth range, that unite with the 

 plates of the vault. 



The vault is broadly convex over the central part and am- 

 bulacral channels and depressed toward the margin in the in- 

 terradial areas. There is a small spine bearing plate in the 

 center of the vault, and one over the junction of the ambula- 

 cral channels in each of the five radial series. The plates are 

 small and the sutures too indistinct, over part of the vault of 

 our specimens, to distinguish them. The azygous orifice is 

 large, surrounded with numerous plates and subcentral. It 



