242 
THE VOYAGE OF H.M.S. OHALLENGEE. 
colour, make tke surface rough, and render the whole colony opaque. On making 
a section of the colony the Ascidiozooids, which are easily removed, are found to lie in 
small cavities separated by narrow partitions formed of test substance and sand grains. 
The Ascidiozooids although small are conspicuous on account of the contrast between 
their light yellow colour and the dark surrounding test. They are placed nearly at 
right angles to the upper surface. The test cells are granular and are generally of 
branched forms, but they are not pigmented and are usually very inconspicuous. 
The mantle is fairly muscular over all parts of the body (see PI. XXXII. fig. 7). The 
branchial aperture is distinctly six-lobed, and the sphincter is well developed. The wall 
of the branchial sac is rather thick and opaque. 
The atrial aperture is circular and has no lobes and no languet. It is placed on the 
dorsal edge at some distance from the branchial aperture. In this respect this species 
resembles the genus A'plidium. 
The stomach is moderately large. It is globular, and has its wall slightly folded 
longitudinally. The spermatic vesicles are of considerable size. They are ovate or 
spherical in form, and the vas deferens is conspicuous. 
Psammaplidium rude, n. sp. (PI. XXXI. figs. 1-4). 
The Colony is an irregularly lobed sandy mass. It is incrusting and is attached by 
a broad base. The upper surface is wide and usually flattened, with low projections or 
knobs. The surface is uneven and rough. The colour is greyish-yellow, the colour of 
the sand. 
The length is about P5 cm., the greatest breadth is 2‘5 cm., and the thickness is 
1’5 cm. 
The Ascidiozooids are not visible on the outside of the colony, and no common 
cloacal apertures are to be seen. The body is about 3 mm. in length and scarcely 1 mm. 
in breadth. The thorax, which is about 1’5 mm. in length, is indistinctly separated 
from the rest of the body. 
The Test contains a large amount of imbedded and incrusting sand, which renders it 
stifi* but Ijrittle and quite opaque. The matrix is clear and structureless. The test cells 
are minute and not very numerous. No bladder cells are present. 
The Mantle is thin and transparent, but fairly muscular. On the thorax the 
muscle bands are mainly transverse in direction, and are branched so as to form an 
irregular network. On the post-abdomen the muscle bands run longitudinally. 
TJie Branchial Sac is large and well developed. The transverse vessels are 
moderately wide, and all of the same size. The stigmata are numerous; they are 
well developed, and are arranged with regularity. The ciliated cells are distinct. 
TJiC Dorsal Lamina is represented by a series of very short stout tentacular languets. 
