1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo oi3 
forskal, Physopsis africana globosa, and Potadoma liricincta major. 
All of these also occur in the Congo basin. 
Moreover, the malacological fauna of the Nile basin as a whole offers 
nothing very distinctive. Throughout its course the river retains the 
usual Ethiopian types, which thus reach the shores of the Mediterranean. 
As first pointed out by Jickeli, the fluviatile mollusk fauna of Lower 
Egypt is distinctly Ethiopian, while the terrestrial forms of the sur- 
rounding country are all of Palearctic affinities. The very few Pale- 
arctic fresh-water types of Lower Egypt, such as the true Physide, 
Lymnea truncatula, and perhaps some of the Unionide, may be of 
quite recent introduction, possibly even brought in by man. At any 
rate they have not yet succeeded in entering the Ethiopian Region by 
way of the Nile 
As compared with that of the Congo basin, the Nilotic fauna is 
chiefly characterized by the extreme poverty in Melaniide, this family 
being only represented by the very widely distributed Melanoides tuber- 
culata and a few Cleopatrxe; the one reported species of Potadoma, if at 
all present, having evidently strayed from the Congq drainage. The 
subgenus Leroya of Lanistes is also absent. On the other hand, the Nile 
basin shows a far greater abundance of Bulinus, Viviparus, Corbicula, 
and Unionide. It possesses but one genus, Planorbula, thus far unknown 
from the Congo system, although one species has been described from 
Lake Tanganyika. ) 
Mollusk Fauna of the Central African Lakes 
The fauna of the Ethiopian Region exhibits on the whole less of the 
exuberance found in other tropical parts of the world. It possesses, how- 
ever, two outstanding features unparalleled elsewhere. The first is its 
extraordinary wealth in Mammalia, in which respect it appears to have 
retained conditions that were more wide-spread during Tertiary times. 
The second is the existence close to the equator of several large fresh- 
water lakes, some of considerable depth and nearly all with a profusion 
of aquatic animals, frequently of most unusual types. During the last. 
sixty years the fauna of these lakes has been rather actively investigated. 
Its peculiar character is well indicated by the following figures taken from 
W. A. Cunnington’s recent review of the subject: ‘Tanganyika contains 
402 species [of all groups of animals] of which no less than 293 are endemic, 
1As noted above, the occurrence of this Potadoma in the Semliki basin is somewhat doubtful. 
2Jickeli, C. F. 1875. ‘Riickblick auf die Land- and Siisswasser-Mollusken Nord-Ost-Afrika’s, 
nebst einigen Bemerkungen iiber die Molluskenfauna Afrika’s.’ Jahrb. Deutsch. Malakoz. Ges., II, 
pp. 334-353. 
