SEMIVERTEBRA TES. 
566 
a jet of water; and that some of them, like the-one figured on p. 561, are used as 
articles of food. To the same subfamily as Phallusia also belongs the extensive 
genus Asciclia, in which the outer tunic is soft and flexible, instead of being 
cartilaginous. A totally distinct subfamily is, however, indicated by the remark¬ 
able deep-sea genus Hypobytliius, of which the two known species were obtained 
at depths varying from six hundred to two thousand nine hundred fathoms, 
during the voyage of the Challenger. Here we find the cup-shaped or pear-like 
pear-shaped ascidian, IIypobythius nat. size). 
body attached by a longer or shorter stem; while the apertures are circular and 
not closed by lobes. The outer tunic is cartilaginous, but soft and thin, although 
thickened in places to form plates. The internal longitudinal bars usually found 
in the branchial chamber are wanting in this genus; the gill-slits are small and 
irregularly placed; and the viscera form a compact irregular mass on the dorsal 
side of this chamber. In the species here figured {H. calycodes), which is from 
the North Pacific, the stem is of great length, and the outer tunic thickened so 
as to form a number of nodules or plates; but in the South Atlantic form (H. 
