1927] Pilsbry-Bequaert,. The Aquatic Mollusks of the Belgian Congo 515 
tremely pronounced; the genera and even the species are often the same, 
notwithstanding the fact that these two ranges are 150 kilometers apart 
and nowadays separated by lowland country covered with savanna and 
partly occupied by a lake. These peculiarities are best understood if we 
admit that during a rather recent glacial period the various life zones 
shifted to a considerably lower level. 
A comparative study of the land mollusk fauna in the several vol- 
canoes, at various altitudes, would be of extreme interest, but unfor- 
tunately we possess hardly any data on which this could be based. The 
lower region of Mt. Mikeno alone has been somewhat more completely 
explored by Robin Kemp. Preston and, more recently, Connolly have 
described from that mountain, between 1,700 m. and 2,000 m., the follow- 
ing species:! 
Burungaélla oscitans Gulella burungaénsis 
. emperforata ‘‘  aridescens curta 
a buhambaénsis ‘¢ — mikenoénsis 
Nakurvélla soror Thapsia inclinans — 
. ahena ee, AOE 
Urguessella capillata . ‘‘  aridescens 
Nothapalus ugandanus Trochozonites expatriata 
-Pseudoglessula burungaénsis “* Africarion”’ copiosus 
se perobtusa ay spatiosus 
tenebrosus 
Cerastus kempi 
Gonaxis buccina 
The very few mollusks recorded from the remaining Kivu volcanoes 
are as follows: 
Mt. Sabinyo Mt. Karisimbi 
Limicolaria saturata, at 3,000 m. Lamicolaria saturata, at 2,400 m. 
Vitrina bambusetz, at 3,000 m. “ Helix’ runssorina, at 3,300 m. 
Vitrina tenuissima, at 3,400 to 4,200 m., 
on leaves of tree Senecio. 
Of great interest is the occurrence of true Vzirzne in the higher 
regions of these two mountains. In both cases, the animal has been 
studied anatomically, so that the generic reference is beyond doubt. 
: 6. East African Highland District 
This district is mainly developed in Tanganyika Territory. ae 
enters the Belgian Congo only on the northeastern shores of Lake Tan- 
ganyika, in the regions known as Urundi and Ruanda and in the valley 
of the lower Ruzizi. It covers there all areas below the 1,400 m. contour 
1The species of Burungaélla, Nakuruélla, and Urguessella appear to be true Helicidz whose relation- 
ship has, however, not yet been investigated. 
