HOLOTHURIOIDEA OF THE INDIAN OCEAN. 59 



this ridge was not clearly seen, but the colour differences 

 between the two surfaces were accentuated, the biviuni turning 

 a chocolate-brown and the trivium a light yellow. Other 

 spirit specimens examined by me, however, are light yellow 

 all over the body, the pedicels being marked out by a light 

 brown ring around the base of each. The bivium is well 

 arched, and the trivium is flattened. The body- wall is 

 extremely thin, and owing to the absence of pigment on the 

 trivium the internal organs can be faintly seen. The anterior 

 end of the body is rounded, but the posterior portion tapers 

 considerably. The mouth is ventral and is surrounded by 

 twenty light yellow tentacles, and the buccal ridge bears 

 numerous small papilloe. The anus is thrown on to the dorsal 

 surface and appears round in the preserved specimen. In the 

 living animal the pulsating anus is alternately pentagonal and 

 rounded. There are five groups of papillae guarding the anus. 

 The pedicels are irregularly scattered, and the sucking discs 

 are apparently not well developed, since the living animal does 

 not appear to use them much. 



Internal Structure. — The calcareous ring is similar to those 

 of the two previous species. A single Polian vesicle and one 

 stone canal are present. The right respiratory tree is larger 

 than the left, and Cuvierian organs are present. 



Spicules. — The spicules in the general integument agree with 

 those of the two previous species. As in H. argus, there are 

 no deposits in the deeper layers of the dermis. The pedicels 

 are strengthened by irregular rods and H-shaped spicules similar 

 in size and shape to those of H. argus, but the larger rods 

 described in the latter species are not present in H. vitiensis. 



General Distribution. — This species has a similar distribution 

 to that of H. marmorata. 



Remarks. — Undoubtedly the three species H. marmorata, 

 H. argus, and H. vitiensis are closely aUied, and it is only with 

 some difficulty that I am able to discover any differences of 

 sufficient value to justify the separation of the three forms. 

 The colour differences are fairly clear if their constancy can be 

 proved I can vouch for the constancy of the colour of 



