410 
THE VOYAGE OF H.M.S. CHALLENGEK. 
body, and are consequently about as far apart as they can possibly be (PI. XL VII. fig. 7). 
They look as if they were extremely contracted, and although no traces of lobes are visible 
they may have been square when opened. Figures 9 and 10 on Plate XLVII. show the 
branchial and atrial apertures seen from the inside. When magnified about 50 diameters 
the brown upper surface of the test is seen to be distinctly roughened, and to consist of a 
yellowish ground mottled with brown and black marks. The lower surface, on the other 
hand, is of a dull black colour throughout. The test is particularly stiff, and seems almost 
horny in texture. The musculature in the mantle is well developed (PI. XLVII. figs. 9, 10). 
The branchial sac has the usual open structure with no true stigmata. The meshes 
are particularly large, and the vessels are wide and membranous. No cilia are visible. 
The endostyle is distinct ; it is of a yellowish colour. 
The tentacles are probably eight in number, four of them long and the other four 
shorter (see PI. XLVII. fig. 9). 
The oesophagus is a plain tube (PI. XLVII. fig. 8). The stomach is globular and 
rather large. The intestine is short and wide ; it forms a narrow loop. The stomach 
and intestine are of a yellowish-brown colour. 
The only reproductive organs present in the single specimen are in the form of a 
mass of mature ova of an orange colour attached to the inner surface of the mantle. 
Possibly this species, on account of the absence of folds in the branchial sac, ought to 
be placed in a separate genus from Bathyoncus, but the single specimen seems somewhat 
distorted, and slight folds may possibly be present, consequently. I have thought it best ■ 
to leave the species in the genus Bathyoncus for the present. 
Styela radicosa {?), Herdman (PL XLIX. figs. 9, 10). 
Styela radicosa, Herdman, Keport upon Challenger Tunicata, part i. p. 163, pi. xxiv. figs. 6, 7. 
This specimen, from Station 163, is very like the specimen described as Styela radicosa 
in the First Part of this Eeport (p. 163, PI. XXIV. figs. 6, 7) in many of its characters, but 
does not agree perfectly in all details. 
The form of the l^ody is much the same (PI. XLIX. fig. 9), but the posterior end is 
not so globular, and the root-like processes of the test are not so well marked. Also, the 
anterior end does not taper so much, and, as a result, the atrial aperture is placed nearer to 
the branchial, which is terminal in Styela radicosa and decidedly on the ventral edge in 
the present specimen. Then, again, the transverse wrinkling of the test is very slight, and 
not so much distributed as in Styela radicosa, and the colour is different. It is much 
darker, being creamy grey in some places and brown in others. It does not become 
paler towards the posterior end as in the case of Styela radicosa. 
The length of the body is 2 '2 cm., the greatest breadth is 1'5 cm., and the thickness 
is 0'9 cm.; hence there is considerable lateral compression. 
