50 
THE VOYAGE OF H.M.S. CHALLENGER. 
Botrylloides nigrum, n. sp. (PL I. fig. 8 ; PI. III. figs. 19-21). 
The Colony is of irregular shape, flat, and spreading. The surface is uneven and 
moderately smooth. The colour is almost black except at the edge of the colony, where 
it is a little lighter. The common cloacal apertures are rather inconspicuous. 
The length of the colony is about 7 cm., the breadth about 1*5 cm., and the average 
thickness about 2 mm. 
The Ascidiozooids are elongated antero-posteriorly, being about 1‘5 mm. in length 
and about 0'5 mm. in breadth. In thin parts of the colony their anterior parts show on 
the surface as dark areas less than 1 mm. in greatest diameter. 
The Test is soft even in its thickest parts. On its thin expanded edges it is of 
a gre 5 nsh colour and semi-transparent, elsewhere it is dark and opaque. The terminal 
knobs of the vessels are conspicuous in the thin marginal portions of the test as 
black, ovate or elongated markings. The test has a gelatinous homogeneous matrix 
in which numerous very minute cells are scattered thickly. Vessels are abundant 
and their swollen ends are very thickly placed close to the surface around the 
Ascidiozooids. 
The Mantle is very thin and delicate. In some parts it is transparent, in others 
pigmented ; the musculature is very slight. 
The Branchial Sac is long and narrow. There are three internal longitudinal bars 
upon each side. The transverse vessels are rather narrow and are all of the same width. 
The meshes are nearly square, and contain each two or three stigmata. 
The Dorsal Lamina is a plain membrane. 
Locality . — Near the Island of Bermuda. 
One large and a couple of small colonies of this species were obtained growing over 
Annelid tubes and Ascidians ^ from shallow water ofif Bermuda. The dimensions given 
in the above description are those of the large colony. 
The dark colour is a striking feature (see PI. I. fig. 8). In the thicker central parts 
of the colony it is almost black. In other parts it is of a dark earthy colour, while the 
expanded edges of the colonies are somewhat variegated, the greyish or opaque white 
test being marked with numerous black spots caused by the terminal knobs of the 
vessels. In the middle of the dark area formed by each Ascidiozooid is found, on close 
examination, a white spot, in the centre of which is seen the open circular branchial 
aperture. 
Under a lens very little of the structure of the Ascidiozooid can be made out from 
the surface. The deeply pigmented mantle forms the dark area, which varies con- 
siderably in size and shape in the case of different Ascidiozooids. It is generally more 
1 Specimens of Clavelina oblonga (see Part I. of this Report, vol. vi. part xvii. p. 246). 
