268 NON-MARINE MOLLUSCA FROM THE SOUTHERN SUDAN. 



square marginal type, though a modification of the lateral is appreciable- 

 earlier in the series. 



Jaio. — Only one side of the jaw is figured. The complete jaw is composed 

 of a total of 19 rather narrow plates set close together. The width of 

 these plates varies but their disposition is not bilaterally symmetrical, 

 there being one broad plate on one side and three on the other. 



Colour. — Dorsum very dark grey, hyponotum dirty yellow turning to- 

 deeper yellow anteriorly. Covered generally with small black spots. Foot 

 sole orange. Tentacles dark grey. 



[The Collection has been presented to the British Museum (Natural History).} 



EXPLANATION OF PLATES 17 & 18. 



Plate 17. 

 Map sliowiug localities of Mollusca, 



Plate 18. 

 Fig. 1. Nodularia (Ceelafura) sabuensts, Preston, sp. nov. External aspect of right valve. 



2. „ ,, „ Internal aspect, showing liiuge. 



3. ,j „ „ Dorsal aspect. Nat. size. — Soba, Blue Niie. 



4. ,, „ cegyiytiaca, CailL, var. shambiensis, Longstaft, var. nov. Ex- 



ternal aspect of right valve. 



5. ,, „ „ Internal aspect of thin shell showing hinge. 



6. „ „ „ Internal aspect of thick shell showing strong 



teeth. 



7. „ „ „ Dorsal aspect. Nat. size. — Lake Sluunbe, Bahr 



el-Gebel. 



8. ,, „ parreyssi, Phil. Internal aspect of shell similar to Philippi's 



figure of type showing hinge. — Ad Duwem. 



9. J, „ „ var. elonr/ata, Longstafi^ var. nov. External aspect 



of right valve. 



10. „ „ ,, var. elongata, Longstaffj var. nov. Dorsal aspect.. 



Nat. size. — Gebel Ahmad Agha. 



11. ^, „ „ var. obliqua, Longstaft", var. nov. External aspect 



of right valve. Nat. size. — S. of Melut. 



12. Nodularia (Lanceolaria) teretiuscula, Phil., var. pallaryi, LongstafF, var. nov. Ex- 



ternal aspect of right valve. 



13. „ „ „ Internal aspect showing hinge. 



14. ,, ,, ,, Dorsal aspect. Nat. size. — Near Mogran. 



15. Streptuxis stidanica, Preston, sp. nov. Front aspect. 



IG. ,, „ Dorsal aspect. Nat. size. — Sheik Tombe. 



17. Seynientitia kanisaensis, Preston, sp. nov. Front aspect. 



18. ,. „ Spiral aspect. 



19. „ „ Basal aspect. — Kanisa. 



