The Non-Marine Mollusca of Portuguese East Africa. 



197 



of the fold on the rectum inside the mantle-cavity described below. The 

 anus is situated to the right of this fold on the top of the lobe. 



The kidney is long, rather narrow, and nearly straight except at its 

 front end, which, on reaching the mantle-edge immediately below the 

 pulmonary orifice, bends round abruptly, in the manner shown in text-fig. 

 25, B. An afferent renal vein runs back along the left edge of the kidney, 

 and another vein conveying blood from the kidney to the heart passes 

 along beside its right edge. No thickened ridge runs along the kidney as 



13 



14 



18 



B C 



Text-fig. 25. — Planorbis pfeifferi Krs., Lorenzo Marques. 



A. Representative teeth from the radula ; X 500. 



B. Roof of mantle -ca\'ity seen from within, showing kidney, etc. (slightly diagram- 



matic) ; X 8. 



C. Columellar muscle, with buccal and penial retractors arising from it ; X 8. 



in Planorharius corneus (Lin.) ; but between the kidney and the rectum 

 there is a longitudinal fold on the roof of the mantle-cavity, such as we 

 also find in Planorharius and Isidora. Opposite to this a similar fold runs 

 along the rectum, curving to the left as it reaches the anus and continuing 

 to the extremity of the branchial lobe. 



Central nervous system. — The arrangement of the principal nerve-ganglia 

 resembles that in Isidora, Planorharius, and Physa,* the nerve-ring being 

 small and the connectives almost as short as in Isidora {Physopsis) glohosa 

 (Morel.) (PI. VIII, fig. 9), although the lateral lobe of the left parietal 

 ganglion is not quite so distinct as in that species The nerve-ring is 

 situated behind the buccal mass, and the buccal ganglia are a little 



* See de Lacaze-Duthiers : Arch. Zool. Exper. et Gen., vol. i, 1872, pis. xix, xx. 



