20 



secondary radials and unites with the convex outer surface of the 

 arms. There are ten arm openings to the vault. There is a single 

 small intersecondary plate, in each area, that is followed by a 

 larger and longer plate, which separates the bases of the arms and 

 unites with the plates of the vault. 



The first interradials are the largest plates in the calyx, they are 

 subpyramidal and terminate in an acute, central point. They 

 broadly truncate the subradials, separate the primary radials, in 

 in some areas, and, in others, both the primary and secondary 

 radials, and are each followed by five or six plates, in the form of 

 a yoke or arch, that reaches down half or more than half the 

 length of the first interradial. They have, therefore, eight, nine or 

 ten sides, depending on whether or not they abut the second 

 primary radials, and whether there are five or six plates in the 

 yoke. The three or four superior plates of this arch separate the 

 secondary radials and are followed by three or four plates that 

 separate the bases of the arms and unite with the plates of the 

 vault. The number of plates in the regular iuterradial areas are, 

 therefore, not quite uniform, and they graduate into the plates of 

 the vault so as to leave no distinct line of separation. 



In the azygous interradial area two plates truncate the sub- 

 radial, one large, the other small. The large plate corresponds 

 with the first plate, in the regular areas, and has only eight 

 sides, one of which rests on a subradial, another against a first 

 primary radial, another against a second primary radial, and the 

 others against five plates, that form a yoke, as in the other areas, 

 except one side of it reaches a subradial and separates the large 

 plate entirely from one radial series. The area is wider than the 

 regular areas and the plates are somewhat larger, but not more 

 numerous. The superior plate in the yoke extends a little higher 

 than the plates in the regular areas, it unites with plates, at the 

 bases of the arms, and others that extend to the vault, as in the 

 other areas, though not exactly in the same order of arrangement. 



The vault is elevated over the arm furrows, convex on the 

 azygous side of the proboscis, but somewhat flattened on the other 

 side. The proboscis is subcentral. The vault is covered by 

 numerous polygonal, highly convex plates and is moderately de- 

 pressed toward the interradial areas. The proboscis is broken off, 

 but so far as preserved, it is small, round and composed of small, 

 highly convex plates. 



