590 Bulletin American Museum of Natural History [Vol. LII1 
Colony of Cabinda to Landana. Its southern drainage comprises the 
Mayombe, in Belgian territory, a heavily forested, hilly country; its 
main affluent is the Lubuzi with the Lukula as a tributary. Little is 
known at present of the mollusk fauna of the Shiloango basin, but it may 
well possess some peculiar types not found in the Congo basin and perhaps 
more closely related to those of the rivers of Gaboon. Recently Dr. H. 
Schouteden has obtained in the Lukula River and some of the smaller 
streams of the Mayombe, certain Melaniide (Potadoma graptoconus and 
P. schoutedenit) which are conspicuously different from those of the 
Upper Congo and more closely related to the species of Gaboon and 
Upper Guinea. 
The other coastal rivers of the Belgian Congo, such as the Moanda 
and the Kumbi, are very small; they are more or less connected by 
swamps or lagoons in the interior. Nothing is known of their mollusks, 
outside the estuarine forms. 
Congo River System 
The Congo River drains an area of approximately 3,690,000 square 
kilometers, the second largest hydrographic basin of the world (Map 15). 
This basin extends beyond the limits of our territory to include the drain- 
age of the Malagarazi River in Tanganyika Territory, much of North- 
east Rhodesia mainly drained by the Chambezi River, the northeastern 
portion of Angola drained by the headwaters of the Kasai, and a large 
part of French Equatorial Africa. Some of the western headwaters of 
the Sanga even reach into Cameroon. 
Most geographers consider the Lualaba as the upper branch of the 
Congo, which gives to the main stream a length of nearly 4,000 kilo- 
meters. This would be much increased if we regard the Chambezi- 
Luapula-Luvua system as the true headwaters. Many of the tributaries 
are also long and sizable rivers. The course of the Congo and its affluents 
is quite peculiar: south, of 5° S. the rivers generally flow due north; 
but between 5° N. and 5° S. their course is sharply deflected toward the 
west, the Congo itself forming near the equator a bow-like bend which 
reaches 2° N. and finally turns due southwest to its mouth. Of the south- 
ern affiuents the Lomami alone keeps a south to north direction through- 
out its course. The northern portion of the basin is much less extensive 
than the southern part. Here the Ubangi and its upper branches, the 
Bomu and Uele, first follow the usual east-to-west direction; but in 
about 19° E. the Ubangi curves southward with a rather abrupt bend and 
thus reaches its confluence a little south of the equator. 
