Agelacrinidae and Lepadocystinae 
435 
Floor plates (plate I, Fig. 8,f 1), forming the lower or thecal side 
of the ambulacral rays, large and extending the entire width of the 
ray. Their general outline is quadrangular. The lateral thirds 
of the width of each floor plate are flat, but the median third is 
distinctly furrowed by the ambulacral groove which is deeper 
toward the mouth but becomes quite shallow near the terminal 
branches. Following the floor plates from the mouth toward the 
extremities of the branches, the distal end of one plate is over- 
lapped slightly by the proximal end of the next succeeding plate. 
In the case of the anterior ray, the floor of the primary part 
appears to be formed by two plates, poorly exposed. The floor 
plates of the first branches are clearly exposed — three forming 
the floor of the right branch, and two forming the floor of the left 
branch. At the end of the left branch, a floor plate on the left over- 
laps a floor plate on the right, thus starting the secondary branches. 
The floor plates of the secondary branches number at least three 
or four, but at the tips of the branches the outlines of the floor 
plates are not clearly exposed, nor are they clearly differentiated 
from the adjacent marginal plates. 
The floor plates of the left primary ray are not exposed but the 
length of this part is sufficient to admit of two plates. The prim- 
ary part of the branch here designated as ray No. 2 appears to 
rest upon two floor plates. The anterior branch of ray No. 2 rests 
on at least four floor plates. The posterior branch of this ray rests 
on three distinctly grooved floor plates, beyond which are two or 
three thecal plates on which the grooving is faint. The anterior 
branch of ray No. 4 is supported on four floor plates of which the 
last is only moderately grooved ; beyond this are about three thecal 
plates, belonging to the laterally elongated marginal series, which 
also show faint grooving. The floor plates of the posterior branch 
of this ray are not exposed. 
None of the floor plates of the right primary ray, or of any of its 
branches, are exposed. 
The entire width of the floor plates is covered by the ambulacral 
rays. The covering plates consist of two conspicuous lateral series 
(plate I, Fig. 8, c, c) — one series on each side of the ray, or of 
its various branches — and of numerous much less conspicuous 
central covering plates, to a large extent also arranged in two 
series, along the median part of the rays. The lateral covering 
plates rest upon the extreme sides of the floor plates. The lat- 
