8 



the azygous area the first secondary radials are axillary and on each 

 proximal side support two tertiary radials and on one distal side a 

 single large tertiary radial and on the other, which adjoins the 

 azygous area, three tertiary radials, which arrangement gives to this 

 ray four arms. One of the lateral rays is constructed in a some- 

 what similar manner, though, on one of the proximal sides of the 

 hrst secondary radials, there are two tertiary radials, and, on the 

 other, there are three, and. on each of the distal sides, there are two 

 tertiary radials, which gives to this ray four arms. In the ray on 

 the right of the azygous area there is a pentagonal plate inserted in 

 the angle formed by the first secondary radials which supports upon 

 each of three sides a single tertiary plate; those resting on the lateral 

 sides are also supported on the first secondary radials, which gives 

 to this ray three arms. In the other lateral ray there is an hexag- 

 onal plate inserted in the angle formed by the first secondary radials, 

 which bears upon one upper side a single plate that supports a sin- 

 gle arm and upon each of two sides a plate that supports a single 

 arm, and upon the other a plate that supports upon each of two 

 sides a plate, that together support a single arm, which gives to this 

 ray three arms. In the ray opposite the azygous area the first sec- 

 ondary radial supports on one side a single secondary radial that 

 supports an arm and the other secondary radial supports two plates 

 that support a single arm, which gives to this ray two arms. There 

 are, therefore, sixteen arms in this species, and sixteen ambulacral 

 openings to the vault, which are very conspicuous in a summit view. 

 The arms are composed of a double series of interlocking plates and 

 each one is in the form of a sharp angular ridge on the lower side. 



In each regular interradial area there are three plates, one follow- 

 ing the other. The first one rests between the superior lateral sides 

 of the first primary radials and extends as high as the third primary 

 radials. The second one extends about as high as the first second- 

 ary radials and the third one curves over the margin of the calyx 

 and unites with the plates of the vault. In the azygous area there 

 are six plates. The first one is in line with the first primary radials 

 and about the same size. It is followed by three plates, the middle 

 one of which curves up out of the calicular cavity and over the mar- 

 gin of the calyx and unites with the plates of the vault. Each lateral 

 one extends about as high as the first secondary radials and is fol- 

 lowed by another elongated plate that curves over the margin of the 

 calyx and unites with the plates of the vault. 



