205 
concave on their inner side. From the oral side only their inner 
point can be observed as a small triangular piece (PI. II. Fig. 1); 
from the dorsal side they are seen as a small oval plate. (PI. II. 
Fig. 5). 
The disk is covered with rather large plates. On the ventral 
side (PI. II. Fig. 2) there are mostly three larger scales, one 
inner and two outer, but sometimes they are arranged in another 
way, e. g. as shown in Fig. 1: a single 
broad plate following the small inner 
plate. Along the five radial depressions, 
where the arms have been lying, there 
are some smaller, elongate plates. On 
the dorsal side (Plate II. Fig. 4) there 
is generally — but not always — a large 
central plate, surrounded by five radial 
plates of nearly the same size, outside Fig. 1. Disk of Microphiura 
... .. . , n , from the ventral side. 25 /i. 
which some smaller plates are iound; 
they are overlapping outwards. The plates are slightly thickened 
along their free edges which are set with small, round grains. 
Also on the mouth-shields a few such grains occur (Plate II. Figs. 
1, 5). The radial shields are very small, irregular, contiguous at 
their base; they are only to be observed, when the disk is seen 
from the side (Plate II. Fig. 3). 
Though no specimen has been found with the disk retained in 
position, it is clear that it lies wholly on the dorsal side of the 
arms, as indicated by the vertical position of the mouth-shields- 
The arms evidently form projecting ridges over its ventral side. 
The ventral plates (PI. II. Fig. 1) are distinet in the whole 
length of the arms. They are pentagonal, with the outer edge 
curved, the inner angle obtuse; they are widely separated, the side¬ 
arm plates joining in the middle line for so long a distance as 
about the length of the ventral plates. Dorsal plates are 
totally wanting. The side-arm plates widen considerably at 
their outer end, the arm joints being thus constricted in their inner 
