_ Pilsbry-B equaert, The Aquatic Mollusks of the Belgian Congo 501 
average altitude of the areas comprised within this district is about 
1,100 m. The Lendu Plateau and Ruwenzori Range, which, of course, 
exceed 1,500 m. in altitude, are not treated here as belonging to the 
Uganda-Unyoro District, but are regarded as outliers of the Eastern 
Montane District. 
The boundaries between the two major subdivisions of the Ethiopian 
Region, as indicated by the limits of the Uganda-Unyoro District, are 
entirely due to climatic conditions. The district under consideration 
covers all portions of the interlake region which still possess a humid, 
tropical climate. There are, as a rule, two rainy and two dry seasons, 
since the district extends about three degrees north and one degree south 
of the equator: Notwithstanding the equatorial location, these seasons 
are fairly well defined and recur at regular intervals: the heavy rains 
generally come in March, April, and May; the lesser rains in November 
and December. The cooler season extends from May till July, while 
January and February are the hottest months. At Entebbe, situated 
close to the equator on the shores of Lake Victoria, the average total rain- 
fall a year was 58.64 inches (1,489.4 mm.) for a period extending over 
nineteen consecutive years. Although April and May were particularly 
wet, with 10.06 inches (255.5 mm.) and 7.79 inches (197.8 mm.) of rain 
respectively, no months were entirely rainless: the driest were July and 
January, with 2 inches (50.8 mm.) and 2.12 inches (53.8 mm.) of rain 
respectively. The difference between the mean temperature of the 
coldest and that of the warmest month, during the period 1901-1918, 
was 1°.6C. (March, 22°.5C.; August, 29°.9C.). The highest tempera- 
ture registered in the shade was, in 1918, 27° .8 C., the lowest 16° .4 C., 
the difference being 11° .4 C. A comparison of these figures with those 
given before for Eala shows that, although Entebbe is fourteen degrees 
farther to the east and about 200 kilometers beyond the eastern limit of 
the Congo rain forest belt, yet the only climatic differences between these 
two localities are a smaller total rainfall and a distinct seasonal distribu- 
tion of the rains at Entebbe. It must, however, be noted that climatic 
conditions vary rather considerably from one locality to another within 
the district here under consideration. Thus, in the portions lying in the 
Belgian Congo the total annual rainfall is on the whole smaller than at 
Entebbe and the division into dry and wet seasons much sharper, so that 
conditions resemble more those prevailing in the Ubangi Savanna Dis- 
trict. At Mahagi (in 2° 21’ N., 31° E.), for example, the mean annual 
rainfall, over a period of 2% years, was 47.11 inches (1,196.5 mm.); 
January was entirely rainless and but 2.28 inches (57.9 mm.) of rain fell 
