15 



high. The superior sides bend upward and the inferior sides curve 

 into the basal depression so that the calyx can be made to rest 

 on a smooth surface on the third radials. Each one supports on 

 each upper sloping side a series of secondary radials the last ones 

 of which support the free arms. 



The first secondary radials are fully as large or larger than the 

 third primary radials, rather wider than high, part of them pen- 

 tagonal and the others hexagonal, and each one abuts upon the 

 first interradial and one of the plates in the second range of in- 

 terradials. The second secondary radials are as large as the first 

 and wider than high, but not of uniform size. The third secondary 

 radials seem to be smaller than the second, but the sutures are 

 anchylosed, or so obscure, in our specimen, that the outlines can- 

 not be accurately determined. Above these the arm bases be- 

 come prominent. There are only ten arms in this species, but 

 they are very large and composed of a double series of interlock- 

 ing plates. 



The interradial areas are not exactly of uniform size nor is it 

 certain that they are filled with the same number of plates. The 

 first interradials are the larger plates in the calyx. Each one has 

 ten sides, is much elongated, rests its lower angle between the two 

 upper sloping sides of two first primary radials, and separates the 

 first secondary radials between its upper lateral sides, and sup- 

 ports upon the two superior faces two rather large and more or 

 less elongated plates in the second range. In some areas these 

 plates are larger than in other areas. In three of the areas, where 

 the sutures are distinct, there are two plates, in the third range, 

 about half the size of those in the second range,- four small plates 

 in the fourth range, six still smaller plates in the fifth range, and 

 eight small plates in the sixth range, that form the top of the 

 calyx between the arm bases and unite with the plates of the 

 vault, in a zig zag line. Whether or not the plates in the other 

 two areas are the same cannot be determined from our specimen. 



The intersecondary areas are short, but almost like the inter- 

 radial areas, in the upper part, and the plates consist of four 

 ranges. The first one, consisting of two plates, rests between the 

 upper slightly sloping sides of the second secondary radials and 

 in line with the third range of interradials; it is followed by four 

 plates in the second range, six in the third range and eight in the 

 fourth range, that unite with the plates of the vault, in a zig zag 



