I OCTACNEMUS 109 
genus Octacnemus, now known in a solitary and an aggregated 
form. It was found during the “ Challenger ” expedition, and was 
first described by Moseley. It is apparently a deep-sea repre- 
sentative of the pelagic Salpidae, and may possibly be fixed at 
the bottom. The body in the solitary form is somewhat discoid, 
with its margin prolonged to form eight tapering processes, on to 
which the muscle-bands of the mantle are continued. The 
alimentary canal forms a compact nucleus, which is attached to 
an apparently imperforate membrane which stretches across the 
body, separating the branchial from the atrial cavities. The 
Fia. 68,—A, solitary form of Octacnemus bythius (after Moseley) ; B, diagram of struc- 
ture of Octacnemus (after Herdman): C, aggregated form of O. patagoniensis (after 
Metcalf). 1, from outside; 2, with test removed ; and 3, with mantle removed. 
a, Anus; adh, area of attachment; at, atrial, and br, branchial aperture ; br-s, 
branchial sac; end, endostyle ; g.s, gill-slits ; 7, intestine; n.y, nerve-ganglion ; 
oe, oesophagus ; ov, ovary ; p.b7, peribranchial cavity ; st, stomach ; s¢ol, stolon. 
endostyle is very short, and the dorsal lamina is also much 
reduced. The reproduction and life-history are entirely unknown. 
The aggregated form consists of a small number of individuals 
united by a slender cord composed of test, body-wall, and endo- 
dermal tissue. Octacnemus has been found! in the South Pacific 
from depths of 1070 and 2160 fathoms, and off the Patagonian 
coast from 1050 fathoms. Two species have been described: 0. 
bythius, Moseley, and O. patagoniensis, Metcalf. Metcalf, who 
has recently investigated the aggregated form (0. patagoniensis), 
considers that the genus is more nearly related to the Clavelinidae 
than to the Salpidae. Possibly its position might be best 
1 See Herdman, Challenger Report on Tunicata, part iii. 1888, p. 88 ; and Met- 
calf, Johns Hopkins Univ. Cire. No. 106, 1893, and Zool. Jahrb. Abth. Anat. 
xiii. 1900, p. 572. 
