192 
THE YOYAGE OF H.M.S. CHALLENGER. 
median line of the dorsum, but ventrally one is placed at some distance on each side of 
the central line. The inner surface of the proboscis is occupied by a firm deep yellow 
horny layer (pharyngeal region), having a dorsal tooth and two prominent lateral 
ridges. 
The first feet do not differ much from their successors, which, w^hen fully developed 
(PI. XXXIII. fig. 3), present dorsally a very long cirrus with a short basal segment, its 
lower region appearing to be smooth in the preparation, while the distal is distinctly 
annulated. The setigerous process of the foot has a prominent conical papilla anteriorly 
and superiorly, the outline from this part sloping downward and inward. The bristles 
are pale, faintly tinged of a light straw colour, shafts and tips alike diminishing from 
above downward. The shafts (PI. XVa. fig. 13, one of the longer forms) present the 
usual dilatation at the end, are devoid of transverse bars, have a slight curve, and are 
quite translucent. The somewhat elongate process has a terminal hook and a spur 
beneath. Instead of the two black spines so common in the Hesionidse, there are five or 
six slender translucent spines. The ventral cirrus is modified into a huge lobe with a 
bluntly pointed tip, the whole being nearly as large as the rest of the foot. 
The stomach and its csecal appendages agree with those of the Syllidse. 
The specimens were sexually mature, two being laden with ova, which filled the 
lateral perivisceral regions. 
In this form the hypoderm is largely developed over the dorsal region, but is com- 
paratively thin on the ventral surface, so that the somewhat small nerve-area is slightl}' 
protected. The ventral longitudinal muscles are flattened, and the oblique are not strongly 
developed, though some of the fibres pass over the outer border of the nerve-area. 
Numerous ova occur in the perivisceral cavity anteriorly, chiefly arranged in a thin layer 
around the proboscis. The chief muscular mass of the latter is lateral, and in the pre- 
paration it is peculiarly waved and frilled. Moreover, this layer tapers off to a hiatus 
dorsally and ventrally, since the hypodermic and cuticular layers wdth an external band 
of transverse muscular fibres alone occupy the middle line. 
At first sight this remarkable form resembles one of the Hesionidse, the long cirri 
and the great size being especially striking ; but a careful consideration of the structuu'. 
of the head and its appendages, the structure of the feet and that of the proboscis 
with its tooth, ten distal and ten proximal papillse, and other points, show that it is 
characteristically Syllidian. Langerhans,^ apparently with reason, widens the original 
description of the genus by Malmgren, by admitting those with indistinctly articulated 
tentacles, but there is some doubt in regard to the species with simple tips to the 
bristles {e.g., Eusyllis kupfferi, Langerhans) which he also includes. The grounds on 
which the latter are grouped with the former do not appear to me to be sufficiently 
reliable. 
1 Zeitschr.f. wiss. ZooL, Bd. xxxiii. p. 549, 1880. 
