29 



separates them on a level with the top of the secondary radials, 

 behind which there is a single large, spinous plate. The arrange- 

 ment of these three spinous plates, over each radial series, is 

 very much like it is in B. trijugis. The plates of the vault are 

 rather large, and four of them bear very strong spines in addi- 

 tion to those above mentioned. The proboscis is subcentral, 

 and probably very much like that in B. trijugis, though the top 

 of it is broken off in our specimen. 



The general form of this species will readily distinguish it from 

 all others that have been described. It is most nearly related 

 to B. trijugis, but in addition to the general form, it may be 

 distinguished by having fewer plates in the interradial and 

 azygous areas and by the plates of the vault. 



Found by K. A. Blair, in the Chouteau Limestone, at Sedalia, 

 Missouri, and now in the collection of S. A. Miller. 



