PTEROPODA. 11 
conspicuous in the yellow than in the grey specimens. In their natural condition 
the integuments seem to be semi-transparent, especially above the foot, where the 
buccal muscles are often clearly visible. Below the foot they are more opaque, 
but the blackish viscera can be somewhat indistinctly discerned. The shape is 
moderately stout and moderately elongate, either tapering fairly symmetrically to 
the terminal knob, or prolonged into a distinct tail. The majority of the specimens 
have preserved the three larval rings, and when they are absent it seems probable 
that they have been obliterated. The first ring is represented by a circular band 
a little below the mouth, bearing 14-18 whitish prominences set at regular 
intervals. Some distance below the fins and about the middle of the body is the 
second ring, a very distinct line often accompanied by a deep constriction At the 
end of the body is found, with a few exceptions, another deep constriction dividing 
the tip from the rest, so that the animal terminates in a knob, which, in well- 
preserved specimens, is surmounted by a circular frill. 
The fins are of moderate size, transparent, and show inside a network of muscles. 
They are of somewhat varying but rounded outline, and are never triangular or 
quadrilateral. In many cases the base is much narrower than the rest, and this 
feature is probably natural. 
The two anterior lobes of the foot are fairly ample and inclined so as to form 
an acute angle. They are attached to the body only by a narrow base, the greater 
part of the flap being entirely free. The posterior lobe is an acute-angled triangle, 
rather long and thin, but proportionately to the size of the animal larger and stouter 
than in Clione limacina. 
In specimens in which the buccal parts are fully everted there may be seen two 
pairs of tentacles, three pairs of buccal cones, and a pair of hooksacks. The anterior 
tentacles are distinct and fairly large. The posterior tentacles are small, and in most 
specimens can only be found by following the nerves, having become invisible owing 
to retraction. The buccal cones are soft in the best preserved specimens, but very 
distinct. The middle one on either side is the largest. The two which are nearest 
to the foot are set close together, but are separated from the dorsal cone by a 
somewhat larger interval (fig. 11a). The hook sacks, which are not unfrequently 
everted in the form of two bundles, contain 60-70 yellowish hooks, slightly curved and 
somewhat hollowed out on the inner side. They are set in several rows, those at the 
end being smaller than the rest and forming a bundle. 
There are no jaws. The radula (fig. 10) consists of about thirty rows, which have 
a maximum formula of 8. 1. 8, but the median tooth is very small, and is only found 
in one or two of the hindmost rows. Except in this posterior portion, the radula is 
split into two halves, which extend over two protuberances towards the right and 
left, so that the whole organ has somewhat the shape of the letter Y, and in the 
greater part of its length offers no place for a median tooth. ‘This disposition 
was constant in all the radule examined, and seems to be natural and not due to 
