42 



Basals form a low cup, about two and a half times as wide as 

 high, which bears a hemispherical depression tor the attachment 

 of the column. First primary radials transversely concave, large, 

 wider than long, three hexagonal and two heptagonal. Second 

 primary radials quadrangular, about twice as wide as long. Third 

 primary radials about one half larger than the second, three hep- 

 tagonal and two hexagonal, and bear upon each of two of the 

 superior sides two secondary radials, the last ones of which are 

 axillary and, in four of the rays,- support on each upper side two 

 tertiary radials, which gives to each of these rays four arms. In 

 the ray on the right side of the azygous area the distal secondary 

 radial bears, upon each upper side, two tertiary radials, and the 

 proximal secondary radial bears, upon one side, two tertiary radi- 

 als and upon the other a single tertiary radial, which is axillary 

 and bears, upon each upper side, a single quaternary radial, which 

 arrangement gives to this ray five arms. There are, therefore, 

 twenty- one arms in this species. The arm formula is 5+4+4+ 

 4+4. 



In each regular interradial area there are six plates. One in 

 the first range, two in the second, two in the third and one in the 

 fourth, all of which are cut off from any connection with the 

 vault, by the union of the tertiary radials. In the azygous area 

 there are twenty-one plates. The first is in line with the first 

 primary radials and of about the same size. It is followed by 

 three plates in the second range, five plates in the third range, 

 six plates in the fourth, and above these there are five small 

 plates and one elongated plate that extends up to and unites 

 with two plates belonging to the vault. 



The vault is subconoidal and covered with irregular, polygonal 

 plates, and bears a very large, subcentral broboscis. The plates 

 are plain and smooth, except the large plate opposite to the azy- 

 gous side of the proboscis, which is convex. The arm openings 

 are directed upward. No ovarian pores discovered. 



This species caunot be compared with any other twenty- one 

 armed species, unless it is with B. rotundus, and here there is 

 very little resemblance. The form of the calyx is different; there 

 is no constriction in B. roiundus. The vault and proboscis are 

 altogether different, in every respect. This species has twice as many 

 regular interradials and twice as many azygous plates, and the 

 areas are altogether different. It agrees with B. glaber, which is 



