542 Bulletin American Museum of Natural History (Vol. LIIT 
Since large stretches of country within our territory are level, shallow 
depressions permanently filled with water and more or less overgrown 
with aquatic plants are extremely common. Such swamps are of several 
types according to the nature of the vegetation, in relation with the 
depth of the water, altitude, nature and concentration of dissolved sub- 
stances, etc. Sometimes they are so-called mixed swamps, with a rather 
varied flora of hygrophytes (grasses, sedges, marantaceous reeds, Eriocau- 
lonaceze, Melastomacee, etc.), rarely with Sphagnum. A typical example 
of a mixed swamp is shown in Plate LXIII, from a photograph taken 
near Vankerckhovenville, in the northeastern Uele district, April, 1912. 
The groves of wild date-palms (Phenix reclinata) here shown are quite 
characteristic of this environment. Near the margin of these swamps 
there are also thorny bushes of Mimosa asperata. More commonly, 
however, one or a few species of plants predominate in the African 
swamps, such as cattail (Typha): or papyrus (Cyperus Papyrus). 
The papyrusswamps (Pl. LXII, fig.1) are especially characteristic of all 
savanna regions of tropical Africa. They may occupy patches of only a 
few feet square in the quiet backwaters along the banks of rivers or cover 
certain alluvial plains over hundreds of square miles. The huge papyrus 
sedge, or Egyptian bulrush, grows 5 m. to 6 m. high, the culms being about 
3 inches thick at the base. The rootstocks, often as thick as the wrist, are 
so densely matted together that they form a moving carpet, over which 
it is possible, with some care, to walk. Beneath it the water may be many 
feet deep and the bottom of the swamp is a thick layer of oozy, decaying 
vegetable matter. The swamp is often fed by springs and in addition the 
carpet of plants rises and falls with the variations of water level, during 
and after the rains. A good idea of an African papyrus swamp is conveyed 
by Plate LXII, figure 1, from a photograph taken near the sources of the 
Duru River, east of Yakuluku. This picture incidentally shows also the 
generally level condition of much of the Congo-Nile divide, a state of 
affairs not without importance for the at day dispersal of Ethiopian 
fresh-water mollusks. 
Perhaps due to the abundance of decaying vegetable matter, most 
African swamps nourish relatively few species of mollusks. Yet one finds 
here the largest of all fresh-water gastropods, namely most of the species 
of Prla and the Lanistes of the subgenus Meladomus. Pila leopoldvillensis, 
which lives in the mixed swamps near the shores of Stanley Pool, is one 
of the biggest of known Ampullartidee and consequently of all fresh- . 
water snails. 
