Agelacrinidae and Lepadocystinae 
437 
confined to only about four plates, the more distant interambu- 
lacral plates alternating distinctly in all cases. 
Surrounding the central series (plate I, Fig. 8, ia) of large 
squamose, imbricating interambulacral plates, in each division of 
the interambulacral areas, there is a continuous series of much 
smaller bordering plates (plate I, Fig. 8, b), arranged with their 
longer axes more or less perpendicular to the adjoining branches of 
the ambulacral arms. Toward the central part of the theca, these 
bordering plates usually vary from one-third to one-half of a milli- 
meter in length, while the number along the side of the ambulacral 
rays is about equal to that of the adjacent lateral coverings 
plates, or is moderately greater. Usually there is only a single 
series of bordering plates between the various branches of the 
ambulacral rays and the conspicuous plates along the center of 
the included parts of the interambulacral areas. The most con- 
spicuous deviation from this arrangement in a single series is 
found in the anal interambulacral area, which is distinctly wider 
than any of the other areas, and in which the additional space, on 
both sides of the central series of large plates, is occupied by addi- 
tional, but more or less irregularly arranged, bordering plates. 
These bordering plates may be traced almost to the extreme ends 
of the smallest branches of the ambulacral rays, and form the 
readiest guide to the course of the various branches of the rays, 
when the covering plates are absent, since the floor plates here so 
closely resemble the adjacent thecal plates. 
The anus is situated in the posterior interambulacral area. This 
is the area in which the bordering plates, between the large 
squamose central plates and the adjoining branches of the ambu- 
lacral rays are so numerous. The area is rounded oval in form. The 
exact location of the anus is on the right side of the series of large 
central plates, near mid-length of the area. Apparently it is at the 
base of a deep depression but this may be due only to muscular 
contraction on the death of the animal. On the distal side of the 
anus the plates are of small size, gradually merging into the later- 
ally elongate plates belonging to the upper rows of the marginal 
series. If the anus was protected by a pyramid of small plates, 
this pyramid is concealed at present at the base of the anal depres- 
sion. 
The mouth was located centrally. The peristomial plates are 
not preserved in the only specimen known. The lateral covering 
