234 MRS. JAKE LONGSTAFF 0]S^ NON-MAEIXB 



obtained specimens at thirty places^ some o£ whicli were Aasited twice. 

 Though the managers of the steamers were most obliging in trying to suit 

 the tastes o£ all the passengers, these halts were only too few and too short 

 to satisfy collectors, while sometimes the best hunting ground was just dis- 

 covered as the steamer had to. start again. A collection made under such 

 circumstances cannot be exhaustive, and indeed must be regarded only as a 

 contribution towards our knowledge of the Molluscan fauna of the region. 

 The shells were all taken in the river or within one, or at most two, 

 miles from its margin. Many were obtained either by means of a long 

 handled scoop, by boys wading, or in the case of the larger ones, such as 

 ^tlieria, through native fishermen, who caught them in their nets. Others, 

 again, were stranded by the subsiding water of the river, when they often 

 contained the animal alive or but recently dead. Small gasteropods as well 

 as the large Ampullaria were found on marshy ground close by, and the 

 former also on water-plants in the river. 



With regard to distribution it is unnecessary to say much here, as it is 

 given in the notes on each species. It may, however, be pointed out that 

 the range is interesting in a twofold way. 



First, the geographical position of the Nile causes it to carry the drainage 

 of the reoion of the Great Lakes down to the Mediterranean, giving rise 

 to a commingling of Ethiopian and Pala^arctic forms. 



As might be expected, the freshwater molluscan fauna presents, with few 

 exceptions, the same character throughout. But it is otherwise with the 

 land-shells, for Helix desertorum is left behind and distinctly tropical forms 

 take its place. 



Secondly, there is the fact of species extending far beyond the Nile 

 Region over the continent of Africa. Among the bivalves, Sjuitlia ruhens^ 

 for instance, ranges from Lower Egypt to Uganda, and also to Senegal and 

 the Congo ; S. icahlbergi occurs near Khartum and extends thence south- 

 wards to the Transvaal, as well as westwards across to the Ngadda River in 

 Nigeria. And the large gasteropod Biirtoa nilotica extends from the Bahr 

 el-Grebel to Matabele Land in the south, to Lake Tchad in the west, and to 

 the Juba River in the east. 



If we consider merely the district of which I have had a more or less 

 limited experience, we must observe that Cleoj^tatra buUmoides is by far the 

 most frequent and abundant freshwater gasteropod. It occurs in both Palse- 

 arctic and Ethiopian regions, and though so common, is interesting as 

 exhibiting a considerable amount of variation. Ampullaria icernei, a dis- 

 tinctly Ethiopian species, is not only numerous but, on account of its great 

 size, it is also conspicuous. 



As it was the dry season terrestrial gasteropods were scarce, and they were 

 more especially so in 1912, because there had been less rainfall than usual 



