20 



Basals form a round cup about twice as wide as high. It bears a 

 well-defined band, and has an hemispherical depression for the 

 attachment of the column. First primary radials large, a little 

 longer than wide, three hexagonal, two heptagonal. Second and 

 third primary radials together not as large as the first. Second 

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

 primary radials very little larger than the second, one heptagonal, 

 two hexagonal, two pentagonal, axillary, and, in the ra_y opposite the 

 azygous area, bears upon each upper sloping side two secondary 

 radials, which gives to this ray two arms. In each of the other rays 

 the third primary radial bears, upon each upper sloping side, a sin- 

 gle secondary radial, which is comparatively large, axillary and 

 bears upon each upper sloping side a single tertiary radial, except, 

 in the ray adjoining the azygous area, where there are two tertiary 

 radials, which gives to each of four rays four arms. There are, there- 

 fore, eighteen ambulacral openings to the vault, in this species. 

 The arm formula is 4+4+2-f 4-f 4. There is a small intercalated 

 plate above the third primary radial, in the ray on the right of the 

 azygous area, in the specimen illustrated. It is this intercalated 

 plate that makes the third primary radial heptagonal. We suppose 

 this feature to be abnormal, and, therefore, not of specific import- 

 ance. 



There are two plates, in each regular interradial area, one large, 

 the other small and cut off from all connection with the vault by the 

 union of the radials above. In the azygous area there are eight 

 plates. The first one is in line with the first primary radials and of 

 about the same size. It is followed, in the second range, by three 

 plates, and above these there are four smaller ones that are cut off 

 from any connection with the plates of the vault by the union of the 

 second tertiary radials above them. 



The vault is nearly as large as the calyx and bears a very large 

 central proboscis. It is covered by numerous slightly convex 

 polygonal plates. 



This species has its affinities with B. affinis, which is a twelve 

 armed species, B. approximatus, a thirteen armed species, B. ver- 

 neuilianus, a fourteen armed species, B. variabilis, a fifteen armed 

 species, B. cognatus, a sixteen armed species, and B. consanguineus, 

 a twenty armed species. It will be distinguished from these species 

 by the arm formula and eighteen ambulacral openings to the vault. 



