716 
Proceedings of the Royal Society 
end rounded. Attached by a small area a little posterior to the 
middle of the left side. Apertures both on right side, inconspicuous, 
sessile: branchial median and nearly terminal; atrial a short dis- 
tance from the dorsal edge, more than one-third of the way down, 
lobes indistinct. Surface slightly wrinkled and approaching to velvety. 
Colour yellowish-grey or horn-colour. Length, 6 • 5 cm. ; breadth, 4 cm. 
Test rather thin, soft, easily torn, roughish about base of attach- 
ment. Inner surface smooth and glistening; vessels feebly developed. 
Mantle moderately muscular. 
Branchial sac very delicate, minutely plicated; stigmata long and 
thin, eight to twelve in a mesh. Papillae long and curled ; smaller 
intermediate ones also present, and in some places connected by fine 
transverse vessels. 
Dorsal lamina slightly ribbed transversely, with a large tooth at 
the end of each rib and three or four smaller intermediate ones. 
Tentacles filiform, about 24 in number, all the same length. 
Olfactory tubercle longish elliptical, with the opening at the 
anterior end. 
Two specimens from Station 150 (south of Kerguelen Island); 
150 fathoms. 
This species resembles Ascidia tenera considerably in external 
appearance, but is quite distinct. 
Corella japonica, Herdman. 
Three specimens from Kob6, Japan; 8 to 50 fathoms. 
II. Clavelinid^:. 
The little group of Social Ascidians is here placed next to the 
Ascidiadje as a fourth family of Ascidice simplices. The old name 
Clavelintd^e is retained, the only change being that, instead of 
occupying a position intermediate between the Simple and Compound 
Ascidians, they will now be included in the former group. As the 
explanation of my reasons for making this change in classification 
necessitates frequent reference to former observations and theories, 
it is simpler, and seems more advantageous, to give the argument in 
the form of a brief outline of the history of the group. 
