49 



Basals expanded and forming a shallow, hexagonal disc, about 

 twice as wide as the diameter of the column and bearing an hemi- 

 spherical depression for the attachment of the column. First 

 primary radials from one-half wider to twice as wide as long, 

 three hexagonal and two heptagonal. Second primary radials 

 quadrangular, about three times as wide as long. Third primary 

 radials ns small as the second, pentagonal, axillary, and in the ray 

 on the right of the azygous area supports on each upper sloping 

 side two secondary radials, the last ones being axillary and sup- 

 porting on each proximal side two tertiary radials and on each 

 distal side a single, axillary, tertiary radial which supports on 

 each upper side a quaternary radial, which arrangement gives to 

 this ray six arms. In the ray, on the left of the azygous area, 

 the third primary radial supports on each upper sloping side a 

 single, axillary, secondary radial, which bears ou each proximal 

 side two tertiary radials and on each distal side two tertiary 

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

 sloping side, a quaternary radial, which gives to this ray six 

 arms. In the ray opposite the azygous area, the third primary radial 

 bears, upon one side, two secondary radials, the last being axillary 

 and supporting, on each upper side, two tertiary radials, and upon 

 the other side, a single secondary radial, which is axillary and 

 supports, on one side, two tertiary radials, and, upon the other, 

 three tertiary radials, which gives to this ray four arms. One of 

 the lateral rays is constructed in the same way and has four arms. 

 The otlier lateral ray bears upon each upper side of the third 

 primary radial two secondary radials, the last ones being axillary 

 and supporting, on each upper sloping side, two tertiary radials, 

 which gives to it four arms. There are, therefore, twenty-four 

 arras in this species. The arm formula is 6+4+4+4+6. 



The regular interradial areas differ from each other, but none 

 of them connect with the plates of the vault. In each of two areas 

 there are three plates, one followed by two in the second range. In 

 another area there are four plates, one followed by two in the 

 second range, and one in the third range. In the other area 

 there are five plates, one followed by two in the second range, one 

 in the third range and one in the fourth range. There are nine 

 plates in the azygous area. The first one is in line with the first 

 primary radials, and rather larger than either of them. It is fol- 

 lowed by four plates in the second range, and three in the third 

 range, above which there is a single plate that separates the 

 quaternary radials and unites with the plates belonging to the 

 vault. 



—7 



