554 P. CHALMERS MITCHELL. 
and the others be numbered in the usual way, the formula of 
the tentacular arrangement is 1, 0, 4, 0; 3, 0, 4, 0, 2, 0, 4, 0, 
3, 0, 4, 0, 1. 
These ninety-six tentacles, as I have before stated, are all of 
nearly the same length. The inner circle tentacles are rather 
stouter and broader, but this is not a very obvious distinc- 
tion. 
At one region the tentacles of every order were rather 
smaller and more closely packed. The tentacles at the other 
end of the diameter passing through this region were slightly 
larger and more loosely arranged. In the absence of the usual 
oval shape of the oral aperture a very definite axis of symmetry 
seemed to pass through these two regions. The tentacles 
at one end of this apparent axis were much more closely set, 
and appeared smaller ; the tentacles at the other end were large, 
well separated. At the one end the characteristic arrangement 
of the tentacle groups was obvious; at the other it was only 
after repeated counting and marking that it was possible to 
make it out. There was no evidence that the appearance was 
due to irregular contraction, for the whole oral disc was 
apparently not contracted at all. It was found on dissection 
that this diameter stood in no definite relation to the axis of 
the animal. The appearances were due to local variations of 
growth, which so frequently occur even in the most regular of 
the Hexactiniz. 
The tentacles are short, broad, and thin-walled, and have no 
terminal aperture. On the upper or oral aspect they are 
somewhat flattened. Round the edge of this flat surface are a 
set of rather irregular, rounded, compound protuberances 
(fig. 2). These are hollow, and each protuberance communi- 
cates with the cavity of the tentacle by a single circular aper- 
ture (fig. 3). They are the most striking feature of the 
animal, and upon this feature the generic name Thelaceros! is 
based. 
In fig. 4. is represented a transverse section through a part 
of a tentacle and of one of these protuberances. The histology 
1 Ody, teat; and kepaoc, horned, 
