496 
THE VOYAGE OF H.M.S, CHALLENGER. 
dorsally than ventrally. A slight furrow occurs on the dorsum anteriorly, extending 
from the posterior (right) border of the last thoracic segment forward to the deep 
branchial fissure. Ventrally a median furrow passes from the anus forward to the second 
somite behind the thoracic region, in which it slightly bends to the right, crosses the 
segment in front obliquely to the lateral furrow, and turns upward to the dorsum as 
before mentioned. In one example the ventral median line passes anteriorly to the left, 
so that variation occasionally occurs in this respect. The general colour of the body is 
madder-brown, with a dark speck at each end of the uncinigerous rows. 
By the approximation of the anterior bristle-bundles, the prominent lamellae of the 
cephalic collar are drawn nearer each other than usual in Sabella. The collar, which is 
moderately developed, passes downward wdthout break to the triangular lappets on each 
side of the ventral median line. The lappets are separated by an interval, and reflected 
toward the ventral surface. 
The branchise form a graceful fan — on each side — of from twenty-one to twenty-four 
radioles. The basal region, united by the cuticular expansion, is short. The long 
radioles are more flexible than usual, so that they form a lax brush anteriorly. Each 
has externally, at intervals, a pair of ligulate hypodermic processes (PI. XXXIX a. fig. 2), 
a shorter pair often alternating wdth a longer pair. They are somewhat better developed 
toward the distal region (PI. XXXIXa. fig. 9). Between each pair are two deep brown 
oculi (indicated on both of the previous figures), each of which shows externally a trans- 
parent coat, with a series of facets pertaining to the glassy cone-like bodies beneath, the 
bases of the latter resting on a mass of pigment. Toward the ti]3 of the radiole the oculi 
diminish in size, but have the same structure. The radioles appear to have a bare filiform 
tip, but as none of the examples showed this part in a satisfactory condition, further 
examination is necessary. 
The basal region of the branchim is symmetricall}^ and beautifully striped and mottled 
with madder-brown, and as a ligule comes off between each radiole the effect is increased. 
The general colour of the radioles and other parts in the fans is pinkish-brown, the 
deepest tints occurring on the pinnae. The flexibility of the radioles is apparently due 
to the diminution or alteration of the barred cartilaginous axis. 
The anterior region consists of the ordinary eight segments, one, however, showing 
nine ; the peculiarity in the latter case being, that instead of a dorsal bristle-tuft and 
ventral uncinigerous row, there is, besides the usual bristle-tuft, a ventral one, less 
perfectly formed on the left. The uncinigerous row on the right is ver}^ small. The 
dorsal bristles in the typical forms consist of rather slender forms, with elongated tapering 
tips and a narrow wing on each side (PI. XXXa. fig. 13). The inferior series (PI. XXXa. 
fig. 14) have broader wings and a shorter extremity. Posteriorly both sets have proportion- 
ally broader wings, and the tip is very slightly, if at all, more produced than in front. 
The anterior uncinigerous rows fill up the space between the base of the setigerous 
