198 Transactions of the Royal Society of South Africa. 



distance behind the anterior end of the oesophagus. These ganglia are 

 rather large, rounded, and joined by an unusually short buccal commissure. 

 Digestive system. — The dorsal jaw measures about -45 mm. long, by 

 nearly -2 mm. broad in the centre. Its upper margin is arched, while its 

 lower cutting edge is somewhat irregular. It is moderately thick, with 

 faint vertical striae, and is of a brown colour. The lateral jaws are of about 

 the same length as the dorsal jaw, but are narrower and thinner. 



The radula (text-fig. 25, A) measures about 1-65 X -65 mm. when flattened 

 out. The central teeth are bicuspid, and about as broad as they are long. 

 The lateral teeth are broader and tricuspid, the cusps of both central and 

 lateral teeth being rather short in the specimens from Lorenzo Marques, 

 although they are a little longer in examples from near Durban which in 

 other respects agree closely with those from Portuguese East Africa. The 

 marginal teeth are obliquely elongated, their endocones are split up into 

 three or four narrow cusps, and their ectocones tend to become smaller. 

 They are of the same type as the marginal teeth of Planorbarms, Isidora, 

 etc., and differ widely from those of Planorbis s.s. and Segmentina. The 

 transverse rows of teeth curve slightly forwards on each side. The radular 

 formula is: (13+8+1 + 8+13) X 125. 



The salivary glands are long, rather narrow, and somewhat contorted 

 (PL VIII, fig. 19). They do not pass through the nerve-ring, but unite with 

 each other at their posterior ends. The oesophagus is long and narrow, 

 though sometimes a little swollen near its anterior end. The stomach, 

 which contains grains of sand, is rather short, the anterior part with thick 

 muscular walls being much broader than long. The thin-walled posterior 

 division of the stomach bends downwards, and gives off at its lower end 

 the hepatic duct and the small finger-shaped " pyloric caecum," which is 

 about 1 mm. long. The intestine encircles the stomach, and then describes 

 another loop behind it among the lobes of the liver, before passing forwards 

 as the rectum. 



Chief retractor muscles (text-fig. 25, C). — The columellar muscle is broad, 

 and passes forwards to the foot and the sides of the head. About the middle 

 of its length it gives off from its upper surface the two rather narrow buccal 

 retractors, which arise separately, and the penial retractor, which arises 

 close to the left buccal retractor. 



Reproductive organs (PL VIII, fig. 18). — The hermaphrodite gland is com- 

 pact, and occupies the apex of the spire. The hermaphrodite duct is long, 

 slender, and very little convoluted, but bears towards its posterior end a 

 number of small vesicular outgrowths. The albumen gland is of moderate 

 size. Grains of dark pigment are scattered through the connective tissue 

 which surrounds the hermaphrodite and albumen glands, and these organs are 

 thus easily distinguishable from the more lightly coloured liver which lies 



