134 
THE VOYAGE OF H.M.S. CHALLENGER. 
radula (separated from the tongue and the sheath) was 16'5 mm. by about 12 mm. in 
breadth. On the thirty-eighth row of the tongue there were 117 teeth on each side ; on 
one of the youngest (the seventy-ninth) there were only 118. The teeth showed a clear 
yellow colour, generally darker on the thicker parts. The breadth of the median teeth 
(behind, on the tongue) was about "07 mm., their length '09-'ll mm.; the length of the 
hook of the innermost lateral tooth (behind, on the tongue) was about ‘09 by ‘08 in 
height, that of the six succeeding teeth *16, T8, '2, '22, '235, '25, and the length increas- 
ing to '27 mm. ; the height of the teeth from the sixth was '18 mm. The length of the 
hook of the outermost tooth was about '06 by '044 mim in height ; the following ones 
'068 mm. in length (by '06 in height), '08, T; T, 'll; mm. (by '08 mm. in height), 
'12, T3, '14 mm. (by '01 mm. in height) and '16 mm..., The length of the cuticular 
thickening on the outside of the outermost plate was about '025-'03 mm. The median teeth 
(PI. IV. fig. 27', a\ PL VI. fig. 5, a) are flattened and truncated at both ends, broader behind 
than in front ; the anterior half thicker than the posterior, obliquely inclined in front, 
highest in the middle, forming a strong pointed hook, as also a denticle upon the lateral 
portions, which, are directed obliquely inwards. The first lateral tooth (PL IV. fig. 27, b,b ; 
Pl. V. figs. 7, a, 12, 13), is strong and clumsy, with a shorter base, which bears on the 
outer side a strong denticle ; the hook much smaller than in the succeeding teeth. In 
the next following teeth (Pl. V. figs. 7, b, 8, 9, a, 10; Pl. VI. fig. 5) the base, but especially 
the hook, becomes gradually longer ; in all the succeeding teeth (Pl. V. figs. 14, 16), which 
are the most numerous, they retain the same size, and in the outermost portion of the row — 
about the outer sixth; — they again decrease, (fig. 15).. The body of the teeth (figs. 8-11) is 
strong and compressed ; the longish basal part (fig. 16) is a, trifle broader in front ; in front 
and above on the outside of the body, close to the beginning of the hook, is a strong, obliquely 
flattened, pointed denticle (figs. 7, 8, 9, 10, 14) ; the inner side of the body is smooth 
(fig. 11). The hook is directed obliquely outwards and gradually bent (figs. 9, 10), its 
edges are smooth, and the end is more or less obliquely rounded off ; the upper side is 
obliquely flattened, the under keel-shaped with a furrow along each margin (figs. 8, 10). 
The outermost tooth (figs. 14, a, 15, a, 19, a) is quite small with a short hook, but with a 
strong denticle on the outer side of the body. On the outer side of this last tooth I 
nearly always found one (fig. 14, a) or two (fig. 17, a) thickenings of the cuticle, thin, 
yellowish, and elongated. 1 
The salivary glands are pale yellowish-white, rounded, triangular masses, lying on 
the sides of the oesophagus (Pl. V. fig. 27, c,c), filling up the space between the bulbus 
pharyngeus and the anterior liver mass; the left gland is about 12 mm. long by 5 '5 mm. 
in breadth, and of the same thickness ; the right gland is smaller and broader, 8 mm. 
long, 13 mm. in breadth, and 5 mm. in thickness. In transverse sections their form is 
triangular; the outer surface (fig. 27) is convex and smooth, but divided into lobules by 
1 Hitherto there have been no accurate investigations into the mouth-organ of Onchidium. 
