180 
THE YOYAGE OF H.M.S. CHALLENGER. 
Morchellium, Giard. 
Amaroucium, Milne-Ed wards, Observations, &c., 1842 (in part). 
Morchellmm, Giard, Eecherches sur les Ascidies compos4es on Synascidies, Archives d. Zool. 
exp6r., &c., vol. i. p. 641, 1872 (as a subgenus). 
Colony massive, sessile, or pedunculated. 
Systems compound, irregular, and usually inconspicuous. 
Ascidiozooids elongated but not distinctly divided into regions. Branchial 
aperture six-lobed. 
Test gelatinous or cartilaginous. 
Branchial Sac large and well developed. 
Alimentary Canal usually large. Wall of stomach irregularly thickened. 
Post-Abdomen large, but not distinctly separated from the abdomen. 
This group was formed as a subgenus of Aplidium by Giard in 1872 for. the reception 
of a single species, Morchellium argus, the Amaroucium argus of Milne-Edwards. It 
was characterised by the long, sessile post-abdomen, the compound irregular systems, and 
the areolated stomach. The last feature is an important one which this genus shares along 
with Sidnyum, Synoicum, and Morchellioides. From the first of these forms Morchellium 
is distinguished by its post-abdomen not being separated from the abdomen by any 
constriction, while it differs from the second in having compound irregular systems. 
Morchellioides is separated from all of these by having eight lobes round the branchial 
aperture. 
The condition of the stomach-wall in these four genera is very interesting. In place 
of being thrown into longitudinal or transverse folds it is irregularly thickened, the result 
being the production of a series of knobs or very short caeca projecting outwards (see 
PI. XXV. fig. 3). In the case of Morchellioides affinis these caeca form a system of 
irregular longitudinal lines suggesting that the areolated condition is the result of the 
breaking up of a series of longitudinal folds ; while in Morchellium giardi and Sidnyum 
pallidum they are more irregularly placed. 
Xo species have been added to the genus Morchellium since it was instituted by 
Giard in 1872, and the new species described below belongs to the southern hemisphere, 
and differs very considerably in structure from the type species. The genus may be 
divided as follows : — • 
Morchellium. 
Colony pedunculated. 
I 
M. argus. 
Colony sessile. 
I 
M. giardi. 
