REPORT ON THE CRINOIDEA. 255 
rawsoni is shown in PI. X. fig. 8. The adjacent edges of two contiguous first brachials 
send out short processes which meet one another and rest upon the fused muscle-plates of 
the two radials beneath, so as to cut off a tubular space from the body-cavity. I have 
found nothing like this in either of the other specimens, which have lost all the visceral 
mass together with the second and following brachials (Pl. X. fig. 6). The structure in 
question may be only accidental, or on the other hand it may perhaps have some relation 
to the anal tube. 
The presence of the syzygy between the first and second brachials of Riizocrinus 
renders it a matter of some difficulty to obtain entire specimens, especially of Rhizocrinus 
rawsoni. For the arms break away at this point, carrying with them the entire visceral 
mass. This is the condition of the individuals represented in Pl. X. figs. 1, 6, 8; while 
fig. 20 shows the arm-bases from the second brachial onwards, and the visceral mass which 
they enclose. Two of them have been removed so as to expose the simple digestive 
apparatus, with the oral plates around the mouth and a relatively long anal tube. The 
position of the genital glands in the pinnules borne by the epizygals of the third syzygial 
pair is also well shown. 
I am strongly inclined to believe that the loss of the visceral mass and arm-bases may 
occur and be made good during life. This appears to have taken place in the Havana 
specimen represented in Pl. X. fig. 7. Small oral plates are visible in the centre at a 
point much below their usual level, which is seen in fig. 20; while the second brachials 
are so much smaller than the first that the difference is evidently due to fracture and 
reparation, just as so often occurs on the arms of Pentacrinus and Comatula. But in 
this case all the arms broke away together, carrying the visceral mass with them, so that 
a new one had to be developed within the ring of regenerated arms. Not much is to be 
seen of it, however, except the oral plates, the replacement of which is a point of 
considerable interest. It has long been suspected that eviscerated Comatule have the 
power of restoring their disks; but this is the first instance of the kind that I have met 
with in a Stalked Crinoid. 
Owing to the fact that the ring of anchylosed basals in Rhizocrinus was at first 
regarded as an enlarged top stem-joint, the affinity between this genus and Bourgueti- 
erinus has been supposed to be much closer than can be admitted in the light of our 
present knowledge. For in some respects Rhizocrinus stands farther from Bourgueti- 
erinus than even Bathycrinus does. The fossil genus Mesocrinus,’ although still but 
imperfectly known, is probably nearer Bourgueticrinus than either of these two genera. 
But it appears to differ from them in the smaller size of the upper stern-joints, a point in 
which it resembles both Rhizocrinus and Bathycrinus. In the two best known species 
1 See Marshall, Quart. Journ. Micr. Sci., 1884, vol. xxiv., N. S., pp. 525, 526. 
2 On Two New Crinoids from the Upper Chalk of Southern Sweden, Quart. Journ. Geol. Soc., vol. xxxvii. p. 130, 
pl. vi. figs. 1-7. 
