Agelacrinidae and Lepadocystinae 
447 
slightly above the general convexity of the theca. At their distal 
ends they extend parallel to the marginal series of plates only for 
short distances; the two posterior rays, for about 5 or 6 mm.; the 
left anterior ray, for 3 or 4 mm. ; and the anterior ray, for about 8 or 
9 mm. Then the different rays curve strongly upward and 
around, so that the tips, if extended in a straight line, would strike 
the proximal part of the rays at points nearer than the oral center 
of the theca. The length of these recurved tips of the rays varies 
between 4 and 5 mm. The lateral covering plates are elongate 
triangular, the spaces between the tips being occupied by smaller 
and more centrally located covering plates. Covering plates 
belonging to the central series crowd in locally between the lateral 
plates, especially along the outer or convex outlines of the rays, at 
the points of greatest curvature. Along the inner or concave curve 
of the anterior ray, of the specimen here described, the covering 
plates have been weathered away, exposing the floor-plates of this 
ray. These floor plates are quadrangular in form, are 1.5 mm. in 
length, and 2 mm. in width. Five consecutive floor plates are 
visible. A distinctly defined groove, half a millimeter in width, 
extends along the median line of the floor plates. The lateral 
covering plates rest upon the sides of the floor plates. In the case 
of three of the floor plates, there appears to be a shallow longitudinal 
groove along that side of the floor plate which is on the inner or 
concave side of the curvature of the ray. It is probable that this 
lateral groove extends along the entire length of the ray, and that 
it occurs also on the opposite side of the ray. From the basal part 
of the lateral covering plates along the convex side of this ray, 
there extends a short projection, about two- thirds of a millimeter 
in length, which projects outward and downward at a low angle, 
but sufficient to pass beneath the nearest interambulacral plates. 
These basal projections are narrower than the width of the lateral 
plates and probably offered attachment to the muscles drawing the 
basal projections downward and the tips of the lateral covering 
plates, on opposite sides of the ambulacra, away from each other. 
The interambulacral plates are arranged in rows crossing each 
other diagonally. Those in the left posterior interambulacral 
area are best preserved. Their general form is more or less rhom- 
bic, with sufficient of the top and bottom angles truncated in some 
plates to suggest an hexagonal outline. Along the margins of the 
interambulacral areas, the plates are smaller and their outlines 
