374 PALAEONTOLOGY OF ILLINOIS. 



in a direct line, the last one being usually narrow, and 

 partly or entirely wedged in between the brachial pieces so 

 as, in some cases, to separate them a little. Between the 

 first divisions of each ray on the third radials there are 

 usually one or two interaxillary pieces, the first resting 

 upon two short sloping upper sides of the first secondary 

 radials, and supporting the second, which sometimes sepa- 

 rates the brachial pieces a little, while in other instances it 

 is so narrow and short as to allow .them to come in contact 

 over it. (Arms and column unknown.) 



The surface seems to be nearly smooth, or finely granu- 

 lar, and the body plates are nearly even, excepting the 

 secondary radials, which, with the brachial pieces, are 

 sometimes a little tumid, so as to project slightly beyond 

 the plane of the interradial and interaxillary areas, which 

 consequently have a somewhat sunken appearance. 



Hight of body to arm-openings, 1 inch ; breadth, 2.10 

 inches. 



This fine species seems to be most nearly related to B. planodiscus, 

 Hall (sp.), from the Keokuk beds, with which it agrees nearly in form 

 and general appearance. It difi'ers very materially in structure, how- 

 ever, since the rays in that species bifurcate so as to make eight arm- 

 openings to each ray, or forty to the whole series, being just double the 

 number seen in our species. The planodiscus also appears to have the 

 arm-openings directed outward, while the species under consideration 

 belongs apparently to the section of this genus with these openings 

 directed upward. " 



It is an interesting fact, to which our attention has been called by 

 Mr. WACHSMUTH, that not only this species, but several others only 

 found in the very highest part of the Upper Burlington formation, are 

 more nearly allied to species found in the Keokuk beds than to any 

 forms in the Lower Burlington beds. 



Locality and position. Upper bed Burlington division of the Lower 

 Carboniferous at Burlington, Iowa. No. 27 of Mr. WACHSMUTH'S col- 

 lection. 



