1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 507 
invade the temperate mountain region; but Mesafricarion and Helixarion 
are exceedingly numerous in the highlands. Of true slugs the Urocyeli- 
de are abundant, while the Vaginulide do not seem to extend above 1,500 
m. In the Enide we note the absence of Rachis and Pachnodus. 
The peculiar East African element consists of Limicolariopsis in the 
Achatinine; Liobocageia and Subuliniscus in the Stenogyrine; Vitrina; 
Cerastus in the Enid; and a fair number of true Helicidse. As shown in 
the Report of Land Mollusks, these Central African Helices are related 
with the Belogonia Euadenia of: the Oriental Region. With the excep- 
tion of one species of the Ituri Forest (Halolimnohelix langi), they are 
unknown in the Lower Guinea Forest District, but some of them occur at 
rather low altitudes (1,000 to 1,200 m.) in the forest galleries of the 
Uganda-Unyoro Savanna District. Two species have also been described 
from Mt. Cameroon, where a very restricted area possesses some of the 
animals and plants of the Eastern Montane District.! 
The peculiarities of the montane molluscan fauna are still better 
expressed by a detailed examination of Ruwenzori, one of the few areas 
that have been repeatedly visited by collectors and may therefore be 
regarded as somewhat better known, though the 80 species listed from 
the entire range (above 1,500 m.) undoubtedly represent but a portion of 
the fauna. This account will also give an idea of the altitudinal distribu- 
tion of land mollusks in Central Africa in relation with faunal and floral 
life zones.2,>, Mt. Ruwenzori, the third highest mountain of Africa, forms 
between Lakes Albert and Edward a lofty range covering an irregular 
triangle about 80 kilometers long and 40 kilometers wide. It is evi- 
dently due to an upheaval of the eastern escarpment of the Albertine 
Rift which has thrust a central core of greenstones and amphibolite 
through the folded strata of crystalline gneisses and micaschists. It 
consists of six groups of peaks with glaciers, quite distinct from one 
another, the highest reaching an altitude of 5,125 m. To the west it 
slopes very steeply to the Semliki, whose broad and deep valley separates 
it completely from the western escarpment of the Albertine Rift. In the 
east, and especially in the northeast toward Unyoro, the descent is much 
more gradual over the highlands of Toro. 
The base of the mountain (Pl. LVII) and its foothills between 
1,000 m. and 1,500 m. still retain all the faunal characteristics of the 
AAS TAG hoy Beye en ee Naa aa aN SE PT a Sh kN eee ican 
1For this reason J. P. Chapin includes Mt. Cameroon in his Humid Montane Province of the East 
and South African Subregion, erecting for it a ‘Cameroon Montane District.” 
2The known mollusks of Mt. Ruwenzori were all obtained from three valleys: the Mubuku on the 
eastern slope was visited by Woosnam (1906) and the Duke of Abruzzi (1906); the Butagu on the 
western slope, by Stuhlmann (1891), Schubotz (1908), and J. Bequaert (1914); and the Lanuri-Lamia 
on the northern slope, by J. Bequaert (1914). 
