REPOKT ON THE TUNICATA. 
269 
Some of these forms are very closely related to one another. It should be remembered 
that aU the specimens in the collection have been preserved in alcohol, and that some 
of the species, which are now aU of a dull greyish- white tint, may have been distinguish- 
able from one another by their diverse colours when living. 
Leptoclinum tonga, n. sp. (PL XXXY. figs. 1-10). 
The Colony is an irregularly shaped flat expansion, slightly thickened at the edges 
and attached by the greater part of the lower surface. It is of a pure white colour and 
is quite opaque. The upper surface is uneven but smooth. 
The length is about 6 cm., the greatest breadth is about 3 cm., and the average 
thickness is 3 mm. 
The Ascidiozookls are small and not numerous. Their anterior ends are visible as 
minute depressions on the surface, which are arranged in irregular branching lines. No 
common cloacal apertures are visible. 
The Test is solid, firm, and tough. It is opaque, and of a white colour throughout. 
The matrix is homogeneous; it contains a few small fusiform and branched test cells 
and a very large number of calcareous spicules. The spicules are irregularly stellate, with 
the rays usually uneven and blunt at the apex. 
The Mantle is moderately strong. The branchial sphincter is well developed. 
The Branchial Sac is fairly large. There are four rows of long narrow stigmata. 
The Endostyle is large and conspicuous. Its course is straight. 
The Dorsal Lamina is represented by a series of long tapering languets. 
The Tentacles are large and rather numerous. They are of two sizes, but are not 
arranged with perfect regularity. 
Locality. — Station 172, off Tongatabu, Friendly Islands, July 22, 1874 ; lat. 20° 58' S., 
long. 175° 9' E.; depth, 18 fathoms; bottom, coral mud. 
This is a flat incrusting species of a pure white colour. One irregularly shaped 
colony (PI. XXXV. fig. 1) was obtained off the island of Tongatabu in the South Pacific, 
from a depth of 18 fathoms. It was evidently not attached by the whole of the lower 
surface, as the edges are thickened and turned upwards, forming rounded projecting 
margins. The lines produced on the upper surface by the branchial apertures of the 
Ascidiozooids form an irregular network (see PL XXXV. fig. 1), the meshes of which 
project as rounded masses of test. The edges and some other parts of the colony are 
formed of test only, the Ascidiozooids being by no means numerous. The thickness of 
the colony varies from about 1 mm. to 4 or 5 mm. The lower surface by which the 
colony was attached is very finely roughened, and is seen in sections to be produced 
into shorter and longer adhering processes of the test containing each a few spicules (see 
PL XXXV. fig. S,ad., which represents part of the lower surface cut in vertical section). 
