1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 599 
connection is required to explain the presence in Africa of a great series 
of Oriental genera of Zonitide, Enide, Cyclophoride, Viviparide, 
Unionide, etc. In exchange southeastern Asia received genera of Acha- 
tinide, Streptaxide and some other groups from Africa. We strongly 
believe that the African continent, with its great antiquity, Was an 
important autochtonous center of evolution for several groups of terres- 
trial and fluviatile mollusks. In many cases the same genera occur in the 
Ethiopian and Oriental Reigons; in others the genera are distinct but 
closely related. | 
The relations existing between the fresh-water faune of Africa and ’ 
South America have been so fully discussed by H. von Ihering, A. E. 
Ortmann, J. D. Haseman and many others, that we give here only the 
salient points. 
It is generally admitted that, if direct land connection ever existed 
between these continents, it was interrupted before the beginning of 
of Tertiary time. Only the older and more slowly changing groups can 
be expected to show relationship; but groups of great antiquity have had 
time to reach Africa and South America by way of the northern con- 
tinents, so that only such groups as we have reason to believe never 
existed in the north are really significant in this inquiry. 
FRESH-WATER Musseuts.—The affinities of African Unionide are. 
clearly with those of the Oriental Region. The Mutelide, on the other 
hand, have relatives only in South America.? This family is unknown in 
the northern continents, either recent or fossil. Important in this con- 
nection is von I[hering’s discovery of a mussel with the strongly taxodont 
hinge of the Ethiopian genus Iridina, in the Brazilian State of Sao 
Paulo.* 
The highly peculiar family Etheriide has representatives in South 
America, the Ethiopian Region, Madagascar, and peninsular India. It 
has not been found fossil. 
FRESH-WATER GastTROPODS.—The family Ampullariide has in the 
Ethiopian Region one genus, Pila, with calcareous operculum, occurring 
also in Madagascar and the Oriental Region; three genera, Lanistes, 
1The African continent is now generally accepted to have been the center of dispersal of the three 
mammalian orders Hyracoidea, Proboscidea, and Sirenia. See Osborn, H. F.. 1921. ‘ Adaptive radia- 
tion and classification of the Proboscidia.’ Proc. Nat. Ac. Sci. Washington, VII, pp. 231-234. 
2Tf, as A. E. Ortmann claims, Diplodon and its immediate allies belong to the Mutelide, then the 
family includes also all of the naiades of Australia and New Zealand. 
3Unless the Pennsylvanian Triassic Mycetopoda dilucult Pilsbry, 1921, Proc. Ac. Nat. Sci. Philadel- 
phia, p. 36, based on a fragmentary specimen, proves really to belong to this South American genus. 
The generic reference was provisional, as the hinge is unknown. | ; 
4Pleiodon priscus H. von Ihering, 1912, Journ. Ac. Nat. Sci. Philadelphia, XV, p. 489, Pl. xuu, 
figs. 20-23. Unfortunately the age of the deposit containing this mussel has not been determined. It 
is supposed to be Upper Cretaceous or Lower Eocene. 
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