BEVISION OF PALEOZOIC STELLEROIDEA. 103 



Abactinal area of rays with numerous columns of small, more or 

 less tumid, closely adjoining or reticulated, spine-bearing plates. A 

 medial radial and two lateral or supramarginal columns of plates are 

 usually more conspicuous than the accessory columns; however, the 

 radial plates may be also inconspicuous. The longitudinal arrange- 

 ment in columns is usually most pronounced, but sometimes the 

 plates on each side of the radial column may have a decided diagonal 

 arrangement. Small accessory plates are usually inserted between 

 the columns of ossicles or between the individual pieces both distally 

 and proximally. Disk with numerous small accessory plates like 

 those of the rays, with no apparent definite arrangement except 

 the supramarginal columns, which continue over the disk and unite 

 angularly in the axillary areas. The larger plates bear several 

 short articulating spines of which the one on the apex is the largest. 



Ambital areas well developed, there being one or more columns 

 of small plates like the radial accessory columns both in form and 

 arrangement. 



Madreporite usually conspicuous, radially striated, and situated 

 near the margin of the disk between the adjoining columns of supra- 

 marginal plates. 



Inframarginal plates small and numerous distally like the adambu- 

 lacrals, but proximally they usually increase rapidly in width and 

 assist in forming the small interbrachial arcs. Each ossicle has 

 numerous small granules which probably bore short, smooth, articu- 

 lating, blunt spines. 



Adambulacral plates distally like the inframarginals, increasing in 

 width proximally and continuing around the plates of the inter- 

 brachial areas. The two proximal plates of adjoining columns are 

 the paii^s of plates in the oral armature. Each adambulacral plate 

 has a more or less well-developed narrow ambiilacral extension which 

 unites with the carina of the ambulacral plates. These extensions 

 belong to the adambulacral plates, apparently always so distally, but 

 proximally they are often separated from the adambulacral plates 

 by sutures ; throughout the greater portion of the rays they are situ- 

 ated medially, but in the proximal region they are either on the distal 

 or proximal edge, each alternate plate having the extension from 

 the same corner a little longer. Each plate has more or less numerous 

 spine-bearing granules in addition to the three larger articulating 

 spines which are inserted one on the ambulacral and two on the lateral 

 edge. 



Ambulacral furrows generally very wide and regularly tapering. 

 In each ray there are two columns of these plates which are slightly 

 alternating or opposite. The plates are as numerous as those of the 

 adambulacral columns, highly carinated, about as wide as long in the 

 extreme distal portion of a ray, increasing rapidly in width proximally 



