130 
THE VOYAGE OF H.M.S. CHALLENGER. 
Tlie colour of the dorsal surface is bluish-black, the upper side of the head rather more 
brightly coloured ; the upper surface of the rhinophore also of the same colour on account 
of the muscle shining through it, yellowish beneath. The whole under surface of the 
mantle edge and head, the sides of the body, and the foot also, are yellowish. 
The shape of the body is as usual. The dorsal surface is covered with a number of 
rounded greyish simple or granulated tubercles (PL IY. fig. 25 ; PL Y. fig. 2), measuring 
about 3 '5 mm. in diameter, and 1-1 '5 mm. high; among them are a number of smaller 
tubercles ; towards the margin of the back these tubercles become smaller. The eyes were 
hardly distinguishable by a lens ; in transverse sections of the skin they appeared to be 
scattered about singly or united in groups of three or four round a central papilla. The 
thick mantle edge is somewhat thinner, and sinuous in outline at the extreme edge ; 
beneath it is smooth. The frontal shield (Pl. Y. fig. 1) is strong, and crescentic, some- 
what cremate in the middle line, with rounded tentacular edges, at the base of which, 
above and laterally, are situated the nearly cylindrical rhinophoria (fig. 1), which bear 
at their summits the eyes, which were, however, invisible, the rhinophoria being not quite 
protruded. In front of the right tentacle at the upper side of the shield is the short slit- 
shaped orifice of the penis, about 2 mm. wide; at the base of the lower side the perpen- 
dicular mouth-slit with thick folded lips (fig. 1). At the hinder end of the body, at the 
under side of the mantle edge, is the lung aperture (pneumostome), even in its contracted 
state measuring about I mm. in internal diameter, surrounded by thick lips (PL Y. fig. 2). 
On its inner side, at the base of the tail, is the anal aperture, the transverse diameter of 
which is 2 ’5 mm. (fig. 2). Near this last, on the right side, is a little papilla bearing the 
female generative opening (fig, 2). The papilla is continued into a long groove with two 
folds ; this genital groove is prolonged along the low right side as far as the frontal shield, 
and is bent inwards at the root of the tentacle, and can be followed as far as the fine pore 
of the foot gland (situated behind the mouth), which lies deep in the space between the 
head and foot (Pl. YII. fig. 1, b). The foot is strong and broadest in the middle; the 
anterior portion is separated from the head by a space of about 4 mm. ; it has a superficial 
marginal furrow (Pl. YII. fig, 1, a); the upper lip is slightly cleft in the middle line; 
the tail (Pl. Y. fig. 2) is short and flattened, somevyhat pointed, rounded at the end; 
the margins slightly (about 2 mm.) projecting, 
The walls of the body, on the back as well as the foot, are (as much as 5 mm.) thick 
and leathery. The pseudo-peritoneum is quite colourless, the dissepiment behind the 
salivary glands only being slightly grey. 
When the animal was opened, the organs of the body were seen to have the follow- 
ing relations to each other (Pl. V. fig. 27). At the anterior extremity is the mouth-tube 
(fig. 27, a) and the bulbus pharyngeus (b), then comes the oesophagus (d), directed 
obliquely backwards to the left, and on each side of it the yellowish-white salivary 
glands (c, c); after this comes the large dark greenish-grey anterior liver (/), bounded by 
