464 Proceedings of the Royal Society 
membranous on the left side which is large and projecting. Tubes 
very long and diverging at more than a right angle. 
Branchial sac very thick, coarse, and opaque, of a brown colour. 
Plicated longitudinally, and the grooves divided into pouches as in 
the last two species. On the external aspect the wide transverse 
vessels are connected by equally wide irregularly placed longitudinal 
vessels, thus forming a network of quadrangular meshes, each of 
which contains about four rows of stigmata. Meshes on the internal 
surface much elongated transversely, each containing 15 to 20 
stigmata. Papillae at the corners, no smaller intermediate ones. 
Dorsal lamina wide, strongly ribbed transversely, but not pecti- 
nated. 
Tentacles long and stout, about 60 in number, large and small not 
alternating. 
Olfactory tubercle heart-shaped, 3| mm. long. 
Two specimens from Simon’s Bay, 10 to 20 fathoms. 
In both, half the test has been cut away ; the ventral edge, the 
posterior end, and part of each side is wanting. 
This species and the two preceding are allied forms. They agree 
in the great thickness and solidity of the test, in the transversely 
elongated meshes of the branchial sac, and in the absence of small 
intermediate papillae. They also possess that minute longitudinal 
plication of the stigmatic part of the branchial sac which is found in 
two other new species ( Ascidia pyriformis and Ascidia translucida ), 
and on account of which Verrill proposed to separate Ascidia com- 
planata under the generic title of Ascidiopsis. This structure, how- 
ever, is also to be seen in Ascidia mentula , Ascidia sordida, and several 
other species, some of which differ from each other in important points. 
On account of this, I think it unadvisable to use the plication of the 
branchial sac as a characteristic in breaking up Ascidia. If any 
division of the genus is necessary, the three species just described 
form a very natural section characterised by the several points of 
resemblance mentioned above, and worthy of being separated, not on 
account of the similarity in structure of their branchial sacs, but 
because of the remarkable thickness and solidity of their tests sug- 
gesting Pachychlcena (ira %vs and yAcui/a) as an appropriate sub- 
generic name. 
