24 



Basals form a low cup having a round, hemispherical depression 

 below for the attachment of the column. In some specimens the 

 lower part of the cup is rounded into the columnar depression, 

 and upward from it, in others, there is more or less angularity. 

 The cup at the top is about twice the diameter of the column. 

 First radials the largest plates in the body, a little wider than 

 long, three hexagonal, two heptagonal. Second radials small, 

 quadrangular, three or four times as wide as long. Third radials 

 very little larger than the second, pentagonal, axillary and bear 

 upon each superior sloping side, in four of the rays, two second- 

 ary radials, the last ones being axillary and supporting on each 

 upper side two tertiary radials, which gives to each of these rays 

 four arms and four ambulacral openings to the vault. In the ray 

 opposite to the azvgons area, the third primary radial bears 

 upon each superior sloping side three secondary radials which 

 gives to this ray two arms. There are, therefore, eighteen arms 

 and eighteen ambulacral openings to the vault in this species. 

 The arm formula is 4 + 4 + 2 + 4 + 4, and there is no variation 

 among the specimens examined. 



There are three regular interradials in each area, one followed 

 by two more or less elongated plates in the second range, which 

 are cut off from the plates of the vault by the union of the last 

 radials. The first one is in line with the first primary radials and 

 nearly as large. It is followed by three subequal plates, in the 

 second range, and by three plates, very unequal in size, in the 

 third range. Above these, in the fourth range, there are two 

 elongated plates that connect with the plates of the vault. 



The vault is only moderately convex, except near the azygous 

 orifice, where it is elevated more abruptly. It is depressed 

 toward the margin, in the interradial areas. It is covered with 

 smooth plates, some of which are convex. There is no proboscis, 

 though the azygous orifice is somewhat elevated subcentrally. 

 The ambulacral openings are directed upward, at an angle of 

 about forty five degrees, and are seen in a summit view, but are 

 not visible in a basal view of the calyx. No ovarian pores dis- 

 covered. 



This species bears little or no resemblance in general form or 

 surface features to any other eighteen-armed described species 

 and cannot be mistaken for any of them. In form and absence of 

 surface ornamentation and position of the azygous orifice, it re- 



