1927] Pulsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 519 
Jand snails as in the savannas of the Ubangi and Southern Congo 
Districts, since the grass is rather short and spaced, so that the flames but 
rarely scorch the trees and higher bushes. 
Although the molluscan fauna of Katanga has been but very little 
investigated—land mollusks are not known from more than a dozen 
localities—yet it is possible to point out certain peculiarities by which it 
differs decidedly from that of the remainder of the Belgian Congo. 
Perhaps the most interesting is the presence in this area of a series of 
light-shelled, almost transparent Achatine, such as A. greyt, A. nyikaen- 
sis, A. obscura, A. schoutedeni, A. transparens, and A. virgulata. They 
are typical savanna forms, totally different from the heavy, dark-colored 
species met with in the Congo lowland forest. Limicolaria on the whole 
is rare. The curious operculate snail, Tropidophora anceps, which in- 
habits the dry forest savanna, is a typically East African element reach- 
ing in Katanga its extreme western limit. 
_ An interesting assemblage of mollusks was found by the junior 
author on the Kundelungu Plateau, in about 1,800 m. It consisted of 
“Zingis”’ bequaerti, ‘Gonyodiscus’’ ponsonbyt, Gulella haullevillet, and 
Ledoulxia consociata. Unfortunately the radule and anatomy of these 
forms have not been studied, so that it is impossible to know whether the 
“Zingis’’ is a true helicid and whether the species described as ‘‘Gonyo- 
discus’’ has been referred to the correct genus and therefore belongs to the 
Endodontide.! : 
EcoLoGy AND DISTRIBUTION OF FRESH-WATER MOLLUSKS 
The fluviatile mollusk fauna of the Belgian Congo does not lend 
itself to an analysis along the lines we have followed in the foregoing 
study of the terrestrial species. In the present state of investigation 
there does not appear to be any great distinctness in the aquatic faune 
of the several zodgeographic districts. If in a few cases certain forms 
are restricted to one or another of them, it is not quite evident that this 
is not merely due to present-day ecological conditions and has therefore 
no particular zodgeographic significance. -In fact, the outstanding feat- 
ures of the fresh-water malacology of the Congo—and, as we shall see, 
of the Ethiopian Region as a whole—are its poverty in generic and 
specific types and its uniformity over immense areas. 
The fluviatile mollusks recorded at present with certainty from the 
Belgian Congo number 150 species and subspecies (not including those 
1Although no slugs have been thus far recorded from Katanga, the collections made in that region 
by the junior author (1911-1912) included both Vaginulide and Urocyclide. 
