FOSSILS OF THE BURLINGLOX GROUP. 359 



usually about four small pieces occupying ea<-h axillary 

 space of each ray, and often a single range of very small 

 pieces intercalated between the brachials, so as to form, 

 with the latter and the supplementary radial pieces, the 

 under side of the expanded disc. 



Vault nearly flat, or slightly convex in the central region, 

 and a little concave toward the lateral margins ; composed 

 of numerous small, slightly convex pieces of various forms, 

 those near the middle being larger than the others, which 

 become very small toward the margins. These small pieces 

 continue on out so as to cover each of the two main di- 

 visions of each ray, all the way to where they give off the 

 last arms. As these divisions of the rays are produced 

 beyond the general margin of the disc, they give it a dis- 

 tinctly ten angled or rayed appearance, as seen from above 

 or below when the arms are removed. 



Opening of the vault very small, nearly central, and di- 

 rected a little obliquely forward, or away from the anal 

 side ; there being generally a more or less defined depression 

 extending a short distance forward from its anterior side. 



Surface of plates more or less convex, and ornamented 

 by ridges from the central region to the margins, to con- 

 nect with those of the adjacent plates. Where these ridges 

 unite on the center of the iiiterradial and anal plates, they 

 generally form nodes or prominences, but on the radial 

 plates they give origin to a transverse mesial ridge. The 

 radial plates have their costa? or ridges compound, or moie 

 numerous than those of the other plates ; while above the 

 third radials the succeeding secondary, tertiary, and other 

 pieces of the rays, as well as the brachial pieces, have each 

 a single ridge extending along the middle, while the small 

 intermediate pieces are impressed so as to form concavities 

 between the ridges. 



Higlit of the body of a medium sized specimen 1.63 

 inches; breadth just below the disc 1.30 inches; breadth 

 of disc, measuring across between the rays, 2.20 inches ; 



