142 
THE VOYAGE OF H.M.S. CHALLENGER. 
internally. The proboscis is more compressed (laterally) than in the previous forms, 
and circular fibres are not apparent. Externally is a firm layer of chitinous hyaline 
tissue. The inner border of the radiate fibres is generally more translucent than the 
rest, apparently from the action of the light on their curvature. The hypoderm is 
comjDaratively thin and fibro-granular, and between it and the radiate coat is a 
basement-layer. The cuticle is well marked. A ridge occurs internally at each pole, 
the fibres of the radiate coat opposite the larger or inferior ridge being coarsely 
arranged. Two nerve-trunks appear on each side, about a third removed from the poles. 
They lie, as usual, at the inner border of the hypoderm, i.e., next the radiate coat or 
its basement-tissue. 
Thalenessa oculata, n. sp. (PI. XXL figs. 1, 2 ; PI. XXIII. fig. 12 ; PI. XXV. fig. 3 ; 
PI. XIIIa. figs. 11, 12). 
Habitat . — One example w^as dredged at Station 162 (off East Moncoeur Island, 
Bass Strait), April 2, 1874 ; lat. 39° 10' S., long. 146° 37' E.; depth, 38 fathoms ; surface 
temperature, 63°'2 ; sea-bottom, sand and shells. 
A second (imperfect) specimen occurred in the dredge at Station 172 (off Nukalofa, 
Tongatabu), July 22, 1874 ; lat. 20° 58' S., long. 175° 9' E.; depth, 18 fathoms; surface 
temperature, 75°’0 ; sea-bottom, coral mud. 
The species is of considerable size, the former fragmentary example .measuring about 
55 mm. in length, and with the bristles 6 '5 mm. in diameter. 
The head (PL XXL fig. 2) is distinguished by the very large size of the eyes, 
which are close together on each side, though the pairs are widely separated transversely. 
The anterior pair are the larger, and show a considerable pale area or “ lens.” In the 
smaller example from Tongatabu (PL XXI. fig. 1) the large anterior eyes present a 
peculiar appearance from the obliquity of the pigmentary semicircle (which is pointed in 
front) and the great size of the external pale region. The anterior margin of the head 
has a pair of short antennae with somewhat blunt points, and behind them a median 
tentacle of nearly the same length, and having a similar blunt tip. Each of these 
processes are narrowed at the articulation near the base. This type of tentaculiferous 
head therefore differs from that seen in Stlienelais hoa, with its great median tentacle 
and small antennae. The proboscis in the larger example is extruded, and forms a 
smooth rounded bulla anteriorly. 
The scales, which are comparatively thin, do not cover the dorsum anteriorly, and 
are considerably smaller than those usually seen in this region in the group. As indi- 
cated in the figure (PL XXL fig. 1) of the example from Tongatabu, the scales are 
prettily dappled with brown. The first scale is small, rounded, simply granular in 
