42 
THE VOYAGE OE H.M.S. CHALLENGEE. 
The Mantle is thin, hut moderately muscular. It is very transparent. The muscle 
hands are very narrow, and run most of them in a transverse direction. 
The Branchial Sac is of considerable size and fairly strong. The transverse vessels 
are narrow and all of one size. The internal longitudinal bars are of moderate strength. 
They are rather irregular in their course. The meshes are slightly elongated transversely, 
and contain each about four stigmata. 
The Endostyle is narrow, but is conspicuous through the mantle. It is long and 
straight. 
The Dorsal Lamina is a plain membrane with neither marginal teeth nor transverse 
ribs. It is usually, however, somewhat corrugated or crimped at its margin. 
The Tentacles are sixteen in number. Four are very long and meet in the centre of 
the branchial aperture when laid flat. Four others alternating with these are about half 
as long, while the remaining eight are very short. 
The Dorsal Tubercle is a small aperture with prominent edges placed a short distance 
in front of the anterior end of the dorsal lamina. There is usually no well-marked 
peritubercular area. 
Locality. — Station 208, January 17, 1875 ; lat. 11° 37' N., long. 123° 31' E.; depth, 
18 fathoms ; bottom, blue mud. 
Only one specimen of this large and handsome species was obtained. It occurs growing 
over a very irregularly shaped mass of sponge trawled from 18 fathoms, at Station 208, 
near the Philippine Islands. The colour is a striking feature (PI. I. flg, l), and ig 
probably not very different from what it was when living. The darkest areas are those 
which lie between the rows of branchial apertures and are formed by the posterior parts 
of the Ascidiozooids. The anterior ends are decidedly lighter coloured (PL I. flgs, 2, 3), 
and show the circular open branchial apertures clearly. Under a lens or low power 
objective they also show the anterior extremity of the endostyle (PI. I, fig, 3), the 
peripharyngeal band, the nerve ganglion, and an inner circle, which seems to be the 
line of insertion of the sixteen tentacles, having four marks, placed, one dorsally, one 
ventrally, and two laterally — these are probably the bases of the four largest tentacles. 
Further from the branchial aperture may be noticed three short radially directed lines 
upon each side ; these are probably the anterior extremities of the internal longitudinal 
bars of the l)ranchial sac. Over the whole of this anterior end of the Ascidiozooid little 
clumps of pigmented blood-corpuscles may be found scattered irregularly. From this 
description of the figure (PI. I. fig. 3) it is obvious that a considerable amount of the 
anatomy of the Ascidiozooid may be made out simply from a surface view slightly 
enlarged. This is very rarely the case with alcoholic specimens of Compound Ascidians. 
In some parts of the colony the Ascidiozooids are arranged in small nearly circular 
or elliptical systems, which suggest the arrangement in the genus Botryllus, but in other 
