136 
THE VOYAGE OF H.M.S. CHALLENGER. 
is a somewhat lancet-shaped, short, flattened tentacle, attached to a basal process. 
It does not reach the middle of the peduncles of the ommatophores. The head forms 
a proportionally small and somewhat elongated area, divided into two lobes by a 
slightly elevated median raphe running from the base of the tentacle backward to the 
nuchal collar. Just in front of the base of each ommatophore is the antenna, which has 
a short and somewhat constricted basal segment and a slightly tapered column with a 
dilated terminal boss furnished with a filiform appendage. The dilated boss scarcely 
reaches the tip of the ommatophore. The column of the organ is pale brownish. The 
palpi are comparatively slender, regularly tapered towards the tip, which is slight!}" 
bulbous, and then suddenly filiform. The enlarged region is brownish. The first foot 
is turned forward, and bears the tentacular cirri, which are longer than the antennae, but 
possess the same shape and filiform distal process. They have a brownish belt, partly 
on the dilated terminal portion and j^artly on the end of the column. 
The acute forward prolongation of the snout gives the mouth (which is a longitudinal 
fissure) a characteristic appearance on the ventral surface (PI. XXL fig. 5). The anterior 
part of the fissure extends forward into the narrow region of the snout, while the posterior 
end is opposite the fourth setigerous segment. A beautifully regular series of furrows 
curves outward from the fissure, the majority of the lines having a more or less 
backward direction. The ventral furrow is deeply marked, an interrupted median 
ridge (much elevated in front) occurring in the groove, which commences opposite the 
tenth setigerous segment. The elevated region on each side of the groove is trans- 
versely furrowed, a conspicuous ridge, generally somewhat bifid at the inner end, 
occurring towards the posterior part of each segment. 
The scales are imperfectly preserved, but a considerable number remain on the 
fragment. In regard to arrangement, the first and second scales of opposite sides 
slightly touch at the back of the head, though perhaps they and the third cover the 
region much more in life. The rest widely diverge. The first scale is irregularly quad- 
rate in outline, the anterior margin having a series of clavate j:)apillae, which diminish in 
size from the outer to the inner margin. The processes on the anterior edge (PI. XXV. 
fig. 4, representing a few of the outer) are irregularly lobed, and the majority are 
slightly branched. The hypodermic cells are well marked at the margins of the terminal 
lobes, and they are also very distinct over the area of the scale, which is variously folded 
and wrinkled. The second (right) scale has its outer margin provided with simple and 
rather broad clavate processes. The other scales have a smooth margin, and are large, 
rounded lamellae, the surface of which is studded over with minute papillae, and here 
and there with large, clear, hypodermic areolae. When viewed in profile, the papillae 
are low and flat, and appear almost like undulations on the surface. The brownish 
pigment has a dotted appearance under a lens, since it is absent from the clear papillae. 
The first bristle-bearing foot carries dorsally the papilla for the first scale. The 
