REPORT ON THE CRINOIDEA. 91 
others rather resemble Rhizocrinus and Bathycrinus in the arrangement of the digestive 
tube. Pentacrinus decorus is one of the latter. Even at the level of the radial axillaris 
the gut appears in section as a simple, but spacious cavity, with slight extensions at two 
points round the connective, or rather calcareous, tissue in which the plexiform gland is 
embedded. But it could hardly be called kidney-shaped, as it is in Rhizocrinus and 
Bathycrinus. 
Some sections of a Pentacrinus disk, that were made for Sir Wyville Thomson by 
Dr. Stirling, show the indentation of one wall of the gut at the level of the radial 
axillaries by the plexiform gland and its surroundings to be considerably more marked 
than in Pentacrinus decorus (Pl. LVI. fig. 4)‘ I am unfortunately unable to determine 
the species, as the sections were not properly labelled, and the series is not sufficiently 
complete for the purpose. 
In Pentacrinus wyville-thomsoni, however, the condition of the gut is much more like 
that found in Antedon, which it further resembles in its disk being somewhat more inde- 
pendent of the skeleton than in other Pentacrinidee. Even at the level of the second 
radials, a horizontal section of the disk shows a strong concavity at one side of the gut, 
which is thus almost crescentic in outline. The plications of the inner wall, however, 
are by no means so well developed as they are in many Comatule. 
In the remarkable genus Actinometra, the radial centre of the water-vascular system 
does not correspond with that of the dorsal skeleton; and the curious duality of the 
Crinoid organisation is thus seen more distinctly in this type than in any other. The 
mouth is not sub-central but excentric, or even marginal (Pl. LXI. fig. 2), and there is 
no regular symmetry in the distribution of the ambulacra (PI. LV. figs. 1, 2; Pl. LVI. 
fig. 7). The mouth may be radial, as in all endocyclic Crinoids, and such species of 
Actinometra as Actinometra solaris, Actinometra pulchella, and Actinometra jukesi 
(Pl. LY. figs. 1, 2); or it may be interradial, as in Actinometra magnifica (PL LVI. 
fig. 7); while in some types its exact position is difficult to determine. This is, 
however, immaterial as regards the course of the digestive tube, which proceeds directly 
downwards to a point somewhat behind and on the left (east) of the centre of the disk, 
and then commences to wind. 
Its direction, just as in the endocyclic Crinoids, follows the watch-hand when seeu 
from the ventral side; but there are four coils instead of one. This is shown in fig. 3, 
where the + at the end of the first coil marks the termination of that part of the gut 
which represents the whole digestive: tube in the endocyclic forms. 
This first coil occupies the extreme edge of the lowest part of the disk, and consequently 
passes in front of the mouth, so as to appear beneath it in longitudinal section (Pl. LXI. 
fig. 2). The second coil passes immediately behind it, and is followed by two more in an 
ever narrowing but ascending spiral, which terminates in the more or less central anal 
1 This figure nearly corresponds to the southeast corner of Pl. VIIb. tig. 7. 
