PTEROPODA. 11 



conspicuous in the yellow tlian 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 radulse examined, and seems to be natural and not due to 



