28 



supports on one upper sloping side three secondary radials and 

 upon the other two secondary radials, the last one being axillary 

 and supporting upon each upper side two tertiary radials, which 

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

 nineteen arms and nineteen ambulacral openings to the vault in 

 this species. The arm formula is 4 + 4+3+4+4. 



All of the iuterradial areas are cut off from the vault. In each 

 of the regular interradial areas there are three plates, one, fol- 

 lowed by two in the second range. In each of the other two 

 regular interradial areas there are four plates, one, followed by 

 two in the second range and by one in the third range. In the 

 azygous area there are eleven plates. The first plate is in line 

 with the first primary radials and nearly as large. It is followed 

 by three plates in the second range, four in the third range, two 

 in the fourth range and one in the fifth range, which is cut off 

 from the vault by the union of the second tertiary radials. 



Vault highly convex or obconoidal, covered with smooth polygo- 

 nal plates, and bearing a subcentral proboscis. The ambulacral 

 openings are visible in a summit view. No ovarian pores dis- 

 covered. 



This species bears little or no resemblance in general form or 

 surface features to either B. attenualus or B. nodnlosus, the other 

 two nineteen-armed species heretofore described from the Burling- 

 ton Group, and cannot be mistaken for either of them. In its 

 smooth surface and general form its afiinities would seem to be 

 with B. rotimdus, B. oblatns and B. eiiodis, above described. 

 This species, however, has only nineteen ambulacral openings to 

 the vault, while B. rotundus has twenty-one, B. chlaius twenty- 

 two and B. cnodis twenty-three. This, alone, is suflicient to dis- 

 tinguish the species. They differ further in the azygous and reg- 

 ular interradial areas, and this species bears a large subcentral 

 proboscis, while B. ohlntus and B. enodis do not bear any, and 

 B. rotundus bears a very small one. 



Found in the Burlington Group, at Burlington, Iowa. The 

 specimen illustrated is in the collection of A. Albers, and other 

 specimens are in the collection of S. A. Miller. 



