THE MOLLUSCS OF THE GREAT AFRICAN LAKES. 203 



ganglion. 5. Cerebral ganglion. 6. Left pleuro-subintestinal ganglionic 

 trunk. 7. Pallial nerve. S. (Esophagus. 9. Superintestinal ganglion. 



10. Osphradial nerve. 11. Siphon. 



Fig. 6. — Nervous system dissected from the right side. 1. Buccal mass. 

 2. Buccal ganglion. 3^ Cerebral ganglion. 4. Pedal ganglion. 5. Pleuro- 

 subintestinal trunk. 6. Otocyst. 



Fig. 7. — Section through cerebral ganglion, showing — 1. Cerebral ganglion. 

 2. Pleuro-pedal connective. 3. (Esophagus. 4. Anterior otocyst nerve. 

 5. Calcareous bodies in connective tissue. 6. Otocyst with otoliths. 



Fig. 8. — Section through osphradium. 1. Osphradial nerve. 2. Osphra- 

 dial epithelium. 3. Osphradial ganglion. 



Figs. 9 — 11. — Sections showing relation of the cerebral and pleural ganglia 

 (see text). 



PLATE 12. 



Figs. 12 — 20. — Variations and polymorphs of shell of Typhobia Horei 

 (see text). 



Figs. 27, 28.— Typhobia shells at time of birth. 



Figs. 29, 30.— Shells of Bathanalia Howesi. 



Fig. 31. — Animal of Bathanalia removed from shell. 1. Operculum. 



Fig. 32. — A single row of teeth from the radiila of Bathanalia. 



Fig. 33. — Base of shell of Bathanalia, showing the open columella. 



PLATE 13. 



Fig. 34. — Nervous system of Typhobia Horei, viewed from above. 

 1. Buccal nerves. 2. Tentacular nerves. 3. Optic nerves. 4, 5, 6. Cerebral 

 ganglion. 7. Otocyst. 8. Nerve from pleural ganglion, which does not form 

 a right pallial anastomosis. 9. Pleural ganglion. 10. Right pallial nerve. 



11. Visceral nerve. 12. Superintestinal ganglion. 13. Branch of visceral 

 nerve. 14. Left visceral nerve. 15. Superintestinal commissure. 16. Co- 

 lumella nerve. 17. Left pleural nerve going to form left pallial anastomosis. 



Fig. 35.— Nervous system of Typhobia Horei, viewed from the side. 

 1. Buccal nerve. 2. Cerebral ganglion. 3. Pleural ganglion. 4. Super- 

 intestinal commissure. 5. Right pallial nerve. 6. Otocyst nerves. 7. Co- 

 himella nerve. 8. Pleural nerve, going to form pallial anastomosis. 9. Left 

 pleural ganglion. 10. Otocyst. 11. Pleuro-pedal connective. 12. Lateral 

 pedal nerves. 13. Great anterior pedal nerves. 14. Ladder-like connections 

 between the bases of the great anterior pedal nerves. 15. Superintestinal 

 ganglion. 17. Osphradial nerve. 18. Right visceral nerve. 19. Left visceral 

 nerve. 20. Cerebro-pedal connective. 



