124 Transactions of the Royal Society of South Africa. 



External features of the animal (PI. V, figs. 4-6). — The foot-sole is tri- 

 partite, owing to the presence of a pair of longitudinal grooves. The foot 

 is truncate at the hind end, and has a caudal mucous pore, over which 

 there projects a short pointed caudal lobe. The foot-fringe is rather broad, 

 and bounded by a conspicuous peripodial groove. Above this there is 

 another peripodial groove, separated from the lower one by a single row of 

 rugae. A rather irregular, median posterior groove is present, and oblique 

 grooves slope down from this to the upper peripodial groove. There is 

 no keel. A well-marked lateral groove runs down on the right side of the 

 head, but the dorsal grooves and the left lateral groove are less conspicuous. 



The body-lobes are broad, the left being undivided, and rather narrow 

 shell lobes are also present. The exact form of these pallial lobes will be 

 seen from fieures 4 and 5. 



A B 



Text-fig. 4. — Helicarion {Gymnarion) nyasanus Smith, Macequece. 



A. Representative teeth from the radula ; X 250. 



B. Central tooth from the radula of another specimen ; X 250. 



The animal is of a hght colour, except for two dark bands which run for 

 a short distance along the sides of the hind end of the foot. The thin skin 

 over the upper part of the liver and kidney is almost entirely covered with 

 opaque white pigment, and white flecks seem to be scattered over the roof 

 of the lung, and even on the under-side of the kidney. This organ appears 

 to be long and narrow, but unfortimately the pallial organs of the two 

 specimens examined were not sufficiently well preserved for further 

 description. 



Digestive system. — The jaw (fig. 8) is very pale brown, and about 2 mm. 

 long. It has a prominent projection in the centre, but is otherwise smooth, 

 excepting for the lines of growth. 



The radula of the larger specimen examined (text-fig. 4, A) measures 

 4-7 X 2-2 mm. when flattened out. The central and lateral or admedian 

 teeth are tricuspid ; the endocones, however, tend to become united with 

 the mesocones in the outer lateral teeth. The marginal teeth, which are 

 twice as numerous as the laterals, are mostly unicuspid, having single, 

 long, narrow cusps ; but in the three or four transitional teeth next to 



