512 Bulletin American Museum of Natural History (Vol. LIII 
to twenty miles from the shores of Lake Albert, the Semliki, and Lake 
Edward. In about 1°S. it crosses the floor itself of the Rift by way of the 
Mfumbiro voleanoes and continues southward along the eastern scarp, 
some 20 miles front Lake Kivu and the Ruzizi River. Near the northern 
end of Tanganyika it turns abruptly to the east on the divide between the 
basin of the Kagera and that of the Malagarazi Rivers.! 
The only important flowing waters of the Nile basin within our terri- 
tory are the Rutshuru, Semliki; and Kagera Rivers and very little is 
known as yet of their faune. The Kagera drains the major part of the 
mountainous country of Ruanda and, like its affluents, follows a tor- 
tuous and often torrential course across this elevated and rugged 
province. At times, however, the valleys broaden out and the stream 
forms small lakes, with swampy shores. The various reaches are also 
often connected: by picturesque falls. One might expect the fluviatile 
mollusks of this region to be of some interest, but the few species 
recorded thus far have been so imperfectly studied that their affinities 
are quite obscure.? 
The Semliki, or ‘‘Semeliki,” as the natives call it (also known in 
certain districts as Issango or Itiri), a river some 260 kilometers in length, 
serves as effluent to Lake Edward which it connects with Lake Albert. 
It flows at first northward and later northeastward through a deep, 
trough-shaped valley some 20 to 30 kilometers wide, between the western 
scarp of the Albertine Rift and the Ruwenzori Range. The valley is but 
slightly hilly, covered with sparsely wooded savanna in the northern half 
and with dense, tropical rain forest between Beni and Boga. Before 
entering Lake Albert through a swampy promontory, the river traverses 
a low, alluvial plain, covered with grass, and evidently quite recently 
raised above the level of the lake. The Semliki is generally narrow, 
rarely over 500 m. wide, with many obstructions in the shape of rapids 
and sand banks. The photograph reproduced on Pl. LXIX, fig. 1, well 
illustrates the aspect of the river in the savanna country south of Beni. 
It is generally so shallow that it can be forded in many places, at least 
at low water. The malacological fauna of the river itself is as yet totally 
unknown and it would be of great interest to investigate in how far it 
differs from that of the lakes it connects and of the Nile proper. The 
following are the only species reported from the territory drained by the 
Semliki: Lymnea natalensis undussume, Planorbis adowensis, Bulinus 
1The Congo-Nile divide is marked by a heavy dotted line on the map of the Lake Region 
published in the Report of Land Mollusks (1919, Bull. American Mus. Nat. Hist., XL, p. 17). 
_ "These Ruanda records are all contained in Thiele; J. 1911. ‘Mollusken der Deutschen Zentral- 
Afrika Expedition.’ Wiss. Ergebn. D. Z. Afr. Exp. 1907-08, III, pp. 175-214, Pls. 1-111. 
