ECHINODERMATA OF THE BRASSFIELD FORMATION 23 
Between the basal radials and the nearest basal supramarginals 
there are one or two narrow, transversely elongated plates. The 
integument of the abactinal part of the disk apparently broke 
loose from the proximal end of rays III and IV, and contracted 
toward the opposite side of the disk, causing the disk plates on 
that side to be thrust more or less beneath the ring of plates 
forming the margin. Possibly the circular plate, marked C in 
the accompanying figure, is the centro-dorsal. Several plates 
of nearly equal size are slightly reniform in outline, but their 
original location is uncertain. Apparently, the remaining plates 
of the disk were of smaller size, some of them much smaller than 
others, but nothing can be said of their arrangement. In the 
accompanying figure the larger cross indicates the center of the 
disk as suggested by the present arrangement of the ring of 
marginal plates. The smaller cross gives another possible po- 
sition for this center, if shrinkage of the integument be supposed 
to have caused a moderate lateral spreading of that part of the 
marginal ring which remained intact. 
Abactinal area of rays consisting distally of three columns of 
plates, the two columns of supramarginals and the intermediate 
column of radials. The radials here are distinctly smaller than 
the supramarginals, forming with the latter transverse groups, 
each consisting of three plates, the spaces in the angles between 
two consecutive radials and the two adjoining supramarginals, 
on each side, being apparently vacant. The distal margin of 
each radial tends to overlap slightly the proximal margin of the 
adjoining radial. The proximal margin of the supramarginals 
tends to overlap slightly the distal part of the two adjoining 
supramarginals, while that part of the lateral margin which 
adjoins the neighboring radial is slightly pointed and tends to 
overlap the margin of this radial. That part of the ray in which 
the column of the radials is distinctly defined forms about seven- 
tenths of its length. Proximally, for the remaining three-tenths 
of its length, it is difficult to determine with certainty which 
plates are to be regarded as belonging to the column of radials. 
In the accompanying figure, on plate V the outlines of the radials, 
in the distal parts of the rays, and also the outlines of the sup- 
