274 
THE VOYAGE OF H.M.S. CHALLENGER. 
provided with tapering rays, while the other half has rounded knobs (see PI. XXXVII. 
fior. ilj sp”). As a general rule the spicules close to the surfaces of the colony are 
sharper, while those in the deeper parts are blunter, but there are exceptions. 
The branchial siphon is very large. It is lined by a thick layer of test containing 
spicules (PI. XXXVII. fig. 10 , hr., and 12 , t. and sp.). The sphincter is of very large 
size {sph.). At its posterior edge on each side a strong band of muscle fibres arises which 
runs downwards over the thorax near its dorsal edge (PL XXXVII. fig. 10), and crosses 
the oesophagus (PI. XXXVII. fig. 13, m.h.) to be inserted into the test below the 
abdomen, and near to the lower surface of the colony. Just after crossing the oesophagus, 
the muscle band is joined by a smaller bundle of fibres which arises from the mantle 
over the posterior extremity of the endostyle (PI. XXXVII, fig. 13). This is in all 
probability, like the corresponding bands in Leptoclinum thomsoni, and those described 
by von Drasche in the case of Didemnoides macroophorum, a system of retractor muscles. 
The branchial sac is particularly large (PI. XXXVII. fig. 10). It is longer antero- 
posteriorly than dorso-ventrally. The three transverse vessels separating the rows of 
stigmata are moderately wide ; they are all of the same size, and are provided with bands 
of muscle fibres (PI. XXXVII. fig. 14, tr.). The stigmatic cells are distinct and regular. 
The endostyle is very large and conspicuous (PI. XXXVII. fig. 10). The dorsal 
languets are larger than the tentacles. They extend nearly to the endostyle across the 
branchial sac (PI. XXXVII. fig. 10). Their bases are united by a band of muscle fibres 
which runs along the median dorsal line of the thorax. The tentacles are fairly numerous 
(PI. XXXVII. fig. 10). The smaller ones are liable to a certain amount of variation m 
number and arrangement. 
The oesophagus runs dorsall}^ from the posterior end of the dorsal edge of the branchial 
sac. It varies somewhat in calibre (PL XXXVII. fig. 10). The stomach lies in the same 
straight fine with the thorax, and is elongated dorso-ventrally. It is not large, and its 
walls show no ridges nor other thickenings. They are lined by long columnar cells 
(PL XXXVII. fig. 10). No reproductive organs were found in any of the Ascidiozooids 
examined. 
Leptoclinum speciosum, n. sp. (PL XXXVI. figs. 1-8). 
The Colony is a flat expanded mass of considerable size. It is thin and incrusting, 
and is attached by the whole of the lower surface. The upper surface is even, and per- 
fectly smooth. The colour is pure snow white. 
The length is about 5 cm., the breadth is 4 ‘5 cm., and the general thickness is about 
2 mm. 
TJie Ascidiozooids are numerous and of fair size. They are closely placed all over 
tlie upper surface of the colony. They are not arranged in definite systems, but common 
