180 Transactions of the Royal Society of South Africa. 



of black are scattered over the skin lining the shell, chiefly in the region of 

 the liver. 



Pallial organs. — The lung is long ; its roof is very thin, and is traversed 

 by a single pulmonary vein without any distinct branches. The kidney 

 is about twice as long as the pericardium. The ureter arises close to the 

 front end of the kidney and is reflexed in the manner usual among sigmure- 

 throus snails. PI. V, fig. 10, shows the disposition of the pericardium, 

 kidney, and ureter in an embryo taken from the uterus. 



Pedal gland. — Instead of being embedded in the muscles of the foot, the 

 pedal gland lies just above them in the lower part of the body-cavity. It 

 is rather long and much flattened, broad in front, but tapering gradually 

 towards the hind end. A brown band runs along the centre of the gland and 

 indicates the position of the duct. 



Central nervous system (PI. V, fig. 16). — The cerebral ganglia are situated 

 above the hind end of the buccal mass. They are broader than long, and 

 are united by a rather thick commissure, the length of which is about equal 

 to the breadth of each ganglion. The buccal ganglia are small and are 

 united by a commissure of about the same length as the cerebral commissure, 

 but much narrower. The cerebro-buccal connectives are long and slender. 

 The cerebral ganglia are united with the pedal and pleural ganglia by two 

 pairs of rather long connectives. As usual, the pedal ganglia are the 

 largest in the ventral group, but the abdominal ganglion is also rather 

 large. The right parietal ganglion, although much larger than the left, 

 is smaller than the abdominal ganglion, with which it is somewhat closely 

 united. The remaining connectives, on the other hand, are rather long, the 

 pleuro-pedal connectives being the longest in the ventral group. 



Digestive system. — The jaw (PL V, fig. 11) is thin, of the usual crescentic 

 form, and about 1 mm. in length. It is crossed by numerous irregular 

 striae or narrow folds. 



The radula (text-fig. 21, B) measures about 2x -85 mm. when flattened 

 out. The central teeth are extremely narrow, with single vestigial cusps. 

 The lateral and marginal teeth are tricuspid, with quadrate bases. The 

 mesocones are large in the lateral teeth, but become smaller in the marginals. 

 The ectocones are uniformly small, but are always quite separate from the 

 mesocones. The endocones are also small, and in the lateral teeth they 

 become more or less united with the mesocones, from the sides of which 

 they appear to spring. The transverse rows of teeth curve slightly forwards 

 on each side of the middle line. The formula of the specimen examined is 

 (32+l-f32)xl02. 



The embryonic radula (text-fig. 21, A) measures about -Sx -35 mm., and 

 its formula is (IT+l-f 17) X 68. The individual teeth are also smaller in 

 the embryo, and a little broader in proportion to their length. The central 



