o06 Bulletun American Museum of Natural History [Vol. LIII 
tane District of Africa are but the remnants of a much more extensive 
and more or less continuous area with a similar, temperate fauna and flora 
that formerly covered a large part of East Central Africa and of the 
eastern Congo basin. 3 
From what we know at present, the land snails of the mountains of 
equatorial Africa appear to belong to widely distributed genera, but their 
species are peculiar to each range. A beautiful example in point is 
afforded by Limicolariopsis. This is evidently a type of achatinine land 
snail derived from lowland Limicolarze under the influence of the 
temperate, moist conditions of the montane district. Its origin might be 
traced to the former period of more extensive glaciation which created 
temperate moist conditions over much of the territory occupied before by 
ordinary, megatherm Limicolariex. With the return of tropical, drier 
conditions, Limicolariopsis migrated to the forest patches of the higher 
mountains giving rise by isolation to a number of “‘representative”’ species 
in the various highlands of Hast and Central Africa. ‘The same process 
appears to have worked with the Cerastus stock but in a much more 
prolific manner, creating numerous species. 
The most striking features of the molluscan fauna of our Eastern 
Montane District are: (1) its remarkable richness in genera, species, and 
individuals as compared with the other districts of our territory; (2) the 
absence or scarcity of a number of typically West African or Guinean 
land mollusks of the neighboring lowland rain forest; and (3) the appear- 
ance of many East African and Abyssinian types. Of the first point it 
will be sufficient to say that it is the only part of the Belgian Congo where 
mollusks are at all sufficiently varied and abundant to fulfill the expecta- 
tions of the collector; and, although its area is very small and but few 
localities (perhaps a dozen in all) have been thus far investigated, yet 
the total number of genera and species recorded from that district is 
larger than that known from the remainder of the Belgian Congo. The 
large Achatinine, which are a characteristic element of the lowland rain 
forest, are represented by but few species in the Montane District (Acha- 
tina osborni at Masisi, in about 1,800 m.; A. grauerz Thiele in Kwidjwi, 
at 1,500 m.; Limecolaria is abundant in a few species up to 3,500 m.). 
Of the smaller Stenogyrine, Ceras, Pseudoglessula, and Curvella are much 
rarer than in the lowlands; but Homorus and Nothapalus are as well, if 
not better, represented. In the Streptaxidze we note the absence of 
Edentulina and the scarcity of Marconia, Gonaxis, and Streptostele; while 
Ptychotrema and Crulella are abundant. In the Zonitide, Thapsia, 
Ledoulxia, and Trochozonites appear to be lowland genera that just barely 
