EEPOET ON THE TUNICATA. 
205 
are of rather large size and of various shapes. In the outer layer they are very numerous 
and closely placed. The brown colour is probabl}^ due to their presence. 
The musculature of the mantle is much more developed than is usual in Compound 
Ascidians. The transverse bands are closely placed, and over part of the thorax they 
form almost a continuous layer. The longitudinal bands are more distant, but they are 
strong. The whole arrangement recalls the musculature of some of the Cynthiidae 
amongst the Ascidiae Simplices. Possibly the stiffness of the outer layer of the test has 
necessitated this excessive development of the muscular system, in order that complete 
contraction of the Ascidiozooid might be effected. 
The branchial aperture is wide, and is surrounded by six slight lobes (PL XXVIII. 
fig. 10 , hr.). There is almost no branchial siphon, and the sphincter muscle is not strong. 
The atrial aperture is provided wdth a large bifurcated atrial languet (PI. XXVIII. 
fig. 10, at.). 
The fine lonoitudinal vessels in the branchial sac are rather wider than the stigmata 
(PI. XXVIII. fig. 9, 1.V.). The transverse vessels have slight horizontal membranes. The 
branchial region of the body is usually about 3 mm. in antero-posterior extent. The 
endostyle is large and conspicuous (PL XXVIII. fig. 10, en.). Its course is undulating. 
The alimentary canal is of considerable size and forms a narrow loop. The wall of 
the stomach is folded longitudinally. The rectum is a long wide thin-walled tube. 
Aplidium leucophceum, n. sp. (PL XXVIII. figs. 5-7). 
The Colony is an irregularly rounded mass, slightly compressed laterally, and attached 
by a smaU area at the posterior end. The upper surface is broad and irregularly convex. 
The low^er end is relatively narrow, and the sides slope outwards and upwards. The 
surface is slightly rough all over. The colour is a dull grey, with pale, circular spots. 
The length is 2 cm., the breadth is 2 ’3 cm., and the thickness is 17 cm. 
The Ascidiozooids are fairly large and numerous. A single large common cloacal 
aperture is present in the middle of the upper surface of the colony, but the Ascidiozooids 
are placed evenly all over the surface, and do not seem to be arranged in systems. The 
Ascidiozooids are about 1 cm. in length and 1’5 mm. in greatest breadth. The thorax is 
separated from the abdomen by a marked constriction. 
The Test is firm, and the outer layer is stiffened by imbedded sand-grains. It is of 
a dark grey colour and nearly opaque. The inner part is of a lighter grey colour, and 
is rather less opaque. The test cells are fairly large and rather numerous, especially in 
the outer layer. They are of all shapes, and are frecjuently much branched. No bladder 
cells are present. 
The Mantle is thick and opaque. The musculature is very well developed on the 
thorax ; both transverse and longitudinal bands are present. 
