206 
THE VOYAGE OF H.M.S. CHALLENGEK. 
The Branchial Sac is fairly large and very well developed. The transverse vessels 
are rather narrow and all of about the same size. The stigmata are large’, numerous, and 
arranged with regularity. 
The Dorsal Lamina is represented by a series of large triangular languets. 
The Tentacles are large. 
The Alimentary Canal is relatively of large size. It forms a long narrow loop. 
The Post- Abdomen is wide but not very long. 
Locality. — Kerguelen Island ; depth, 10 to 60 fathoms. 
This species is very closely allied to A'plidium fuscum, and may indeed turn out to 
be merely a variety of that species. They were both obtained at Kerguelen Island in 
comparatively shallow water. The external appearance is very much the same in the 
two colonies (compare figs. 5 and 8 on PI. XXVIIL), except that the one is of a brown 
colour, while the other is dark grey. In both cases the anterior ends of the Ascidiozooids 
show on the upper surface of the colony as light-coloured areas, and in both minute black 
sand-grains are found adhering to the surface all over. In the present case the colony 
is rather more compressed, and the posterior end is narrower than in the former species. 
The arrangement of the Ascidiozooids is precisely the same in the two cases, but they 
seem slightly larger in the present species, and the thorax is much more clearly separated 
from the abdomen. In some Ascidiozooids the two regions are merely united by a 
narrow neck, consisting of the oesophagus and rectum, which readily breaks. The thorax 
is about 3 mm. in length. 
The test, although it differs in colour from that of A'plidium fuscum, is very similar in 
structure. The outer layer is rather lighter and less opaque, which is probably due to 
the test cells in that region being less granular. 
The mantle is very muscular. The transverse bands are closely placed, but not quite 
so much so as in the case of Aplidium fuscum. The branchial siphon is very short, and 
the aperture is surrounded by six slightly marked lobes (PI. XXVIIL fig. 6). 
The branchial sac is a little different from that of Aplidium fuscum. The stigmata 
are rather larger, and the transverse vessels are narrower (PI. XXVIIL fig. 7, tr.). 
Slightly developed horizontal membranes are present. There is no interruption on the 
dorsal edge of the sac, as the stigmata extend across from side to side continuously 
between the languets (PI. XXVIIL fig. 7). The endostyle is long and rather narrow. 
Its course is undulating. The dorsal languets are slightly longer than the stigmata. 
They are flattened antero-posteriorly, and they taper to narrow points (PI. XXVIIL 
fig. 7, 1). 
The oesophagus is rather wide, and runs straight backwards (PI. XXVIIL fig. 6). 
The stomach is moderately large, and is ovoid in form, with the narrower end anterior. 
Its walls are slightly ridged longitudinally. The first part of the intestine is narrow. 
