The Non-Marine Molhtsca of Portuguese East Africa. 155 



whorls and measures : alt. 10-8, lat. 10-2 mm. A smaller shell, containing 

 nearly 5 whorls, measures 8-6 X 8-6 mm. 



External features of animal. — The foot-sole is bluntly pointed at the 

 hind end, and is inconspicuously divided longitudinally into a median 

 pale area, and lateral more or less pigmented areas, crossed by transverse 

 grooves. Shallow peripodial grooves are present, but as these run along the 

 very edge of the foot there is no distinct foot-fringe. A caudal mucous 

 pore is absent. The top of the hinder end of the foot is bluntly angled or 

 keeled, but the keel is not developed into a serrate crest, as it is stated to 

 be in some species.* A network of irregular grooves divides the skin into 

 numerous small rugae, but larger and more regular grooves are scarcely 

 developed. There is a broad and ill-defined dark band on each side of the 

 head and neck. 



Mantle and pallial organs. — The mantle-edge bears a right body-lobe 

 beneath the respiratory orifice, and two widely separated left body-lobes. 

 There are no shell-lobes. The thin skin covering the mantle-cavity and 

 visceral hump is translucent and unpigmented ; but the dark liver of the 

 upper whorls is largely covered by a white network formed by the branches 

 of the posterior aorta (PI. VIII, fig. 7). 



The kidney is long, and gradually merges in front into the ureter, which 

 passes forward to within a short distance of the mantle-edge, and then 

 abruptly bends round and opens (text-fig. 17, D). From this point a fold 

 passes backwards close to the upper edge of the ureter and kidney, over- 

 hanging a groove which forms an incipient recurrent ureter. This channel, 

 however, is open throughout its length. 



The main pulmonary vein, which runs beneath the ventral edge of the 

 ureter and kidney, receives several short branches at its anterior end ; 

 and other small veins cross the roof of the mantle-cavity below the rectum 

 and near the mantle edge, as shown in the figure. 



Central nervous system (PI. VIII, fig. 6). — The nerve-ring is small and 

 surrounds the oesophagus, salivary ducts, and buccal retractor, being too 

 small to allow the buccal mass to be retracted through it. The large 

 cerebral ganglia are united by a fairly short, but rather narrow, arched 

 cerebral commissure. The buccal commissure is also rather short. The 

 pedal ganglia lie, as usual, close together, and each is obscurely divided 

 by a slight dorsal furrow into a large anterior and a smaller posterior 

 portion. The anterior portions are united by the broad anterior pedal 

 commissure, and bear on their upper sides the otocysts. The posterior 

 portions are united by the narrower posterior commissure. The cerebro- 

 pleural connectives are relatively short, and the visceral ganglia are closely 

 aggregated and somewhat compressed laterally, although they are all quite 

 * See Pilsbr}' : Bull. Amer. Mus. Nat. Hist., vol. xl, 1919, p. 306. 



