208 
THE VOYAGE OF H.M.S. CHALLENGER. 
The single specimen of this species is an irregularly shaped colony rising from a thin 
extended base, which incrusts and unites a mass of shell fragments and other foreign 
bodies. The upper part of the colony has the form of an irregular truncated cone 
(PI. XXV. fig. 15 ) ; there is no lateral flattening. The colony, although of a light colour, 
is very opaque, the Ascidiozooids being visible only near the base of attachment, where 
the test is more transparent, and they come nearer to the surface. They show as light 
vellowish-grey elongated marks upon the semi-transparent hyaline grey test (PI. XXV. 
fig. 15). The surface of the colony is very uneven all over, and some of the foreign 
bodies are imbedded in the test more than half way up from the base. 
The Ascidiozooids though large are not very long antero-posteriorly. They are thick 
and somewhat sausage-shaped (PL XXV. fig. 15). The anterior end is narrow and 
pointed, while the posterior is broad and rounded. The thorax occupies the anterior 
third or rather less, and is of a pale yellow colour, while the abdomen and post-abdomen 
have no clear line of demarcation, and are of a darker colour. The whole body is 'quite 
opaque. The broadest region is towards the posterior end of the abdomen. 
The test is very thick and solid ; it is quite opaque in the upper part of the colony, 
and is only transparent in thin layers in the lower part. The bladder cells are very 
numerous in some places, and reduce the matrix to a reticulum (PL XXV. fig. 16, hl.)\ 
in other parts they are entirely absent, and the matrix contains test cells of various 
kinds. ]\Iany of these are of regular ovate form and are filled with fine granules. 
Probably the opacity of the test is due to the presence of these cells. Here and there 
also groups of small granular cells occur placed close together. They have assumed 
polygonal forms from mutual pressure just as in the case of the similar cells in Atopogaster 
aurantiaca. Vessels are present in the test, they terminate in elongated ovate bulbs 
(PL XXV. fig. 16, tk). 
The mantle is extraordinarily thick and muscular over the branchial part of the body. 
There are powerful bundles running both transversely and longitudinally, and forming a 
continuous muscular coating. This is quite unlike the usual condition in Compound 
Ascidians, and it recalls the condition of the mantle in typical Cynthiidse amongst the 
Simple Ascidiams. 
The branchial sac is thick-walled and opaque. Its most notable features are the 
prominent horizontal membranes and the small rounded stigmata. 
The dorsal languets are numerous and large. Their edges are richly cihated, and at the 
base they become continuous with the horizontal membranes of the transverse vessels. 
The large tentacles are closely placed, and seem almost to fill up the branchial siphon. 
The alimentary canal is wide but not very long. It is of an opaque yellow 
colour. 
Tlie reproductive organs lie in the intestinal loop, and extend beyond it for a short 
di.stance forming a small post-abdomen. Both ova and spermatic vesicles are present in 
