504 Bulletin American Museum of Natural History [Vol. LIIT 
leaves of low bushes on the densely wooded banks of the Loia River, 
between Irumu and Boga, at an altitude of 1,100 m. These lowland 
Helicide are evidently derived from some of the forms from the neighbor- 
ing higher regions, where the family is fairly well represented. 
B. East African Subregion 
5. Eastern Montane District 
This district occupies in the Belgian Congo the Lendu Plateau, the 
Ruwenzori Range, and the highlands around Lake Kivu and to the 
northwest of Lake Tanganyika. It includes all parts of the eastern Congo 
situated above 1,500 m. These regions are characterized by a peculiar 
temperate and moist mountain climate, partly due to their altitude and 
partly to their location close to the equator and near the eastern margin 
of the West African rain forest. In the absence of exact meteorological 
data, it can only be stated in a general way that the absolute and mean 
temperatures are considerably lower than in the lowland forest and de- 
crease steadily with increasing altitude. The summits of the Mfumbiro 
volcanoes are often temporarily capped with snow, while permanent 
glaciers partly envelop the peaks of Ruwenzori. These highlands are not 
only abundantly favored with rains, but in addition the hot winds 
saturated with humidity that blow from the western lowlands, upon 
ascending the slopes of the eastern mountains, rapidly cool off and form at 
a certain level a belt of dense fogs and clouds. Meteorological conditions 
are much the same throughout the year, so that altitude and exposure 
alone determine the differences of temperature, humidity, and light, 
thus producing along the slopes a regular succession of life zones. If 
one adds to this that the nature of the soil is much less uniform than else- 
where in the Congo, and that the country is extremely rugged, one readily 
realizes that this region offers us an extraordinary variety of ecological 
conditions. In fact, it is by far the most fascinating portion of our terri- 
tory and it fully deserves, biologically speaking, the name of ‘‘ Wonder- 
land of the Eastern Congo” which an enthusiastic traveler has recently 
bestowed upon it. Nowhere else does one find so many interesting 
problems of adaptive radiation, isolation, and distribution, so that a 
detailed account is plainly justified. 
The peculiar and intricate topography of eastern Central Africa is 
entirely due to the existence of two great fractures of the earth’s crust, 
so-called rift valleys, which run parallel to each other in a general north 
to south direction. The easternmost of these fractures, or Great Rirr 
VaLLEy, can be followed from northern Palestine, along the Red Sea 
