212 
THE VOYAGE OF H.M.S. CHALLENGER. 
Fragments of Crustacea, Confer vse, Diatoms, and other debris occurred in the intestine. 
In the structure of the body- wall this form approaches Nereis diversicolor, 0. F. Muller, 
rather than Nereis pelagica, Linn., especially in the fold of the ventral muscles and in the 
position of the nerve-cords. The vertical muscles seem to be largely developed. No 
neural canals are visible, but the specimen is too much softened for minute examination. 
The perivisceral cavity is loaded with the debris of cells and granules. 
Nereis [Platynereis) tongatahuensis, n. sp. (PI. XXXIV. figs. 7, 8, 9 ; PI. XVIa. 
figs, 5, 6, 7). 
Habitat. — Dredged at Station 172 (off Nukalofa, Tongatabu), July 22, 1874 ; 
lat. 20° 58' S., long. 175° 9' W.; surface temperature, 75°‘0 ; depth, 18 fathoms. On the 
mud of a coral reef. 
Head very slightly longer than broad, mottled with pigment ; tentacles longer than the 
head ; eyes larger than in the former, and all with lenses. Palpi large, mottled with 
pigment. Tentacular cirri very long, the longest reaching to the fourteenth segment. 
Paragnathi of proboscis minute — I. and II. absent ; III. absent or indistinct ; IV. 
angular patches of very minute points ; V. absent ; VI. rows of minute points in single 
series ; VII. and VIII. form a series of bars of very minute j)oints. The maxillae are 
deep brownish at the tip, straw-coloured at the base. The first segment is longer than 
the next. Both anterior and posterior feet have longer lobes than Nereis hobiensis. The 
anterior dorsal cirri are also longer. Dorsal bristles spinose as in the former ; no other 
form present in the example. The upper series of the inferior bristles have long spinose, 
the inferior short falcate tips. 
The specimen measures about 33 mm. in length, and at its broadest part in front is 
about 2 '5 mm. in diameter. 
The body is widest in front, just behind the head, and gradually diminishes towards 
the posterior end, which, however, is incomplete. Like Nereis dumerilii the feet have 
two pigment-patches, and a smaller exists on the body at their base. Moreover, a distinct 
line of pigment passes from side to side at the latter, the band thus crossing the segment 
nearer its anterior than its posterior border. The dorsum is prominently rounded in 
front from the included proboscis, but has a slight groove throughout the rest of its extent. 
A much more decided median groove occurs, from head to tail, ventrally. The number 
of segments in imperfect examples is of little moment. 
The head (PI. XXXIV. fig. 7) is longer than broad, and about the length of the 
antero-posterior diameter of the first two segments. The tentacles are comparatively long, 
exceeding the diameter of the head, and the tip is filiform. The palpi present the usual 
shape. There are four large eyes, the anterior pair exceeding the others in size, and 
having the lens at the outer and anterior margin. There is also a minute and indistinct 
