A488 Bulletin American Museum of Natural History [Vol. LIII 
A. West African Subregion 
1. Lower Guinea Forest District 
The rain forest of Lower Guinea extends from west to east across the 
basin of the Congo as a continuous belt, approximately four degrees 
north and south of the equator. In its western portion, on the right bank 
of the Congo, this belt is considerably narrowed, being only developed 
north of the equator, where it connects, moreover, uninterruptedly with 
the forests of Cameroon and Gaboon, the latter sending an outlier south- 
ward into the Mayombe district of the Lower Congo. In its northeastern 
corner the forest extends to beyond the 30th meridian and even crosses 
the hot and moist valley of the mid-Semliki to link up with the montane 
forest along the western slopes of Mt. Ruwenzori. South of the equator, 
however, it does not reach much farther than 28° E. and its boundary 
~ here forms a very irregular line as the lowland forest passes without break 
into the montane forest on the western scarp of the Albertine Rift. 
It cannot be too strongly emphasized that the Lower Guinea forest 
forms an uninterrupted wooded area over 2,000 kilometers long, from 
west to east, and, in the Congo, 800 kilometers wide from north to south, 
and is by no means an alternation of forest in the lower portions and 
savannas on the divides between rivers, as has been so frequently asserted. 
Where the rain forest borders on the savanna the limits are generally 
well-defined, though occasionally there may be a transitional zone of 
grass-land or park-land with scattered patches of dense, humid woods. 
Sometimes, too, more extensive tracts of forest appear, under favorable 
local conditions of climate, in certain areas well beyond the boundary 
of the forest belt. A number of such Guinean forest islands are found in 
the Uganda-Unyoro District and shelter in this area many of the most 
typical West African forest plants and animals (see p. 502). As a rule, 
forest galleries extend along all permanent water-courses from the forest 
belt into the neighboring savanna, and in certain places these galleries 
may be so extensive and so numerous as to render the boundary of the 
continuous forest belt indistinct. Yet in many places the outer limit of 
the forest, as observed from the open country beyond, forms a clear-cut 
line, which may be easily followed across the irregularities of the 
topography. 
The climate of the rain forest is characterized by a uniform and fairly 
high temperature and abundant rains equally distributed over the whole 
year. Throughout this region the total annual rainfall varies from 60 to 
80 inches and rainless periods are unknown or very rare and then always 
