1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo ahr 
and thus allow many West African forms of life to extend southward 
much beyond the limits indicated above. The disturbing influence of 
these valleys is well exemplified by the distribution of the tsetse fly, 
Glossina palpalis (Robineau-Desvoidy), a typical West African insect 
which, however, spreads along the rivers of Katanga to about 11° 8. 
latitude. Some land mollusks appear to follow the same rule. Thus, 
among the species collected by the junior author at Lukonzolwa, on the 
shores of Lake Moero at an altitude of about 980 m., (Pseudoglessula 
stuhlmanni, P. lematrer, P. bowvini, Gulella lamyi, Gulella coarti, Marconia 
kivuensis, Kalella barrakporensis, ‘Gonyodiscus” smithi, Subulina leia, 
Streptostele elegans, and Cyclophorus intermedius), there are some which 
are either also found in the West African Subregion or closely related to 
species from that part of Africa. It is therefore important while collect- 
ing in this district to note topographic conditions and altitude of each 
locality. 
The Katanga offers a much greater physical and geological variety 
than is the rule elsewhere in the Belgian Congo. In the north there area 
series of plateaus known as the Biano and Kundelungu, reaching an 
altitude of 1,400 m. to 1,600 m., exceptionally 1,700 m. or even over 1,800 
m. (west of Lake Moero). These plateaus are fairly level at the top and 
almost entirely built of nearly horizontal, Permo-Carboniferous sand- 
stones of continental origin. The upper Katanga, or region of the copper 
mines, is a peneplain of old Palaeozoic, much folded and tilted rocks, on 
the average 1,000 m. to 1,500 m. above sea-level and so completely worn 
down to near level that the divide between the Congo and Zambezi 
River systems is at present hardly to be noticed. The Biano plateau is 
bordered in the north by the Bia Mountains, a series of rugged eleva- 
tions, 600 m. to 1,200 m. high, with outcrops of Archean granites and 
eneisses, amid belts of tilted pre-Carboniferous strata. The Marungu, 
in the northeastern corner between Tanganyika and the Luvua River, 
is a similar but larger mountainous area. Its summits reach between 
1,100 m. and 2,900 m. in height. In some places it develops fairly level 
table-lands, such as that of Massewa, apparently an outlier of Kunde- 
lungu with which it agrees in geologic constitution. 
The climate is everywhere of the typical savanna type and, owing 
to the combination of southern latitude, high altitude, and rocky soil 
conditions, its effects upon plant and animal life are much more pro- 
nounced here than elsewhere within our territory. During the dry 
season, which lasts about six months—from May to October—and is 
practically rainless, the temperature is much lower than during the rains. 
