62 THE VOYAGE OF H.M.S. CHALLENGEE. 



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as possible, and filled up the other half which was still more torn. 1 have only given 

 the bases of the tentacles, as they were either only preserved in short pieces or were torn 

 away close to the body of the animal. 



The pedal disk is much smaller than the oral disk, and is covered with numerous 

 radial ridges, somewhat in the same way as in Polysiiiihonia tuherosa (PI. IX. fig. 5), 

 The wall is smooth and tolerably thick-walled ; its upper part contains a mesodermal 

 circular muscle, which is very weak in proportion to the size of the animal, both in extent 

 and in the number of its bundles of fibrillse and the strength of the single fibres. On 

 the other hand, powerful masses of muscle are accumulated in the oral disk. The latter is 

 covered with deeply sunk furrows, which begin between the bases of the tentacles and run 

 in a radial direction towards the oral opening. The furrows end in the periphery of the 

 mouth, which is somewhat swollen, and at which two adjacent furrows are sometimes 

 united. The swellings between the furrows, which are sometimes narrow sometimes 

 broad, are caused by the deposition of strong mesodermal muscles. Their structure 

 resembles that already described in Ophiodiscus annulatus, except that the bundles of 

 fibrillae are much more numerous, and form a layer which is at least twice as strong. 

 The number of the radial swellings in the well-preserved half amounts to twenty-four, 

 therefore to forty-eight in all. 



There are likewise forty-eight tentacles which spring exactly from the junction of the 

 wall and the oral disk, one of their walls representing a prolongation of the former, the 

 other a prolongation of the latter. The thick muscular cords therefore only pass on to 

 one side of the tentacle walls, whilst the other consists merely of supporting substance. 



Though only a few of the septa were preserved, these were sufficient to show that 

 they are distributed in alternate pairs of muscular and genital septa. The genital septa 

 are thin- walled, whilst the muscular are strengthened by a thick supporting lamella. As 

 there are in aU forty-eight tentacles, the number of the muscular septa also amounts to 

 forty-eight or twenty-four pairs. 



The above statement suffices to prove that Ophiodiscus sulcatus is very closely allied 

 to Ophiodiscus annulatus, but distinguished from it by the absence of annulation of the 

 wall and by the strong formation of furrows in the oral disk. The two forms may even 

 represent one and the same species, and the differences merely arise from diff'erence of age. 

 At any rate they were both taken at a great depth in two localities, geographically not far 

 apart. 



It is also well worthy of our consideration that in no other Actinia did I find the 

 tentacles so shattered as in the two species before me, not even in specimens dredged 

 from stiU greater depths. This may perhaps have to do with the fact that the animals 

 attach themselves to foreign bodies by their muscular tentacles. I have already specially 

 remarked that the tentacles are probably of great length in the Living animal, so that they 

 would be especially adapted for holding on to other objects. 



