This paper deals with the results of investigations made in Lake Yogo in August, 1951, on the nature and distribution of bottom deposits in relation to the kinds and distribution of higher aquatic plants.
The number of stations at which the collections were made were 63 in total, and 35 of them were chosen in securing samples for the analyses of the bottom deposits (Map 1).
Almost the whole extent of the lake basin is covered with the bottom deposits of mainly soft grey ooze in which silt and clay are confined to the ratio of about 70 % in composition.
The lower limit of the vertical distribution of higher aquatic plants is met with at a depth of 6.5m. Their standing crop in a unit area of bottom varies widely with either depth or location (Table 2). The richest plant growths are observed in the northern part of the lake, at the strata between the depths from 2 to 2.5m, where the biomass in dry weight being estimated as 467 g/m² in maximum and 107 g/m² in minimum. The dominant species of plants are found in the genera Hydrilla and Potamogeton, both of which grow only on the muddy bottom.

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Some of the data for Earth tide observed near the sea have shown the strange results, contrary to our expectancy that the earth surface tilts chiefly with the tidal load of the sea water. We compare the both tidal variations in the discharge rates of hot springs and the observed anomalies of Earth tide in Beppu which were investigated in detail by Dr. E. NISHIMURA, and conclude that the main parts of the latter may originate from the variations in the thickness of the artesian aquifer with the tidal changes in the ground water pressure. It is, thus, inferred that.a few similar phenomena observed in Japan may also refer to the elastic deformation of the artesian aquifer.

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Soné-numa is a small and shallow basin located close to the east coast of Lake Biwa and is analogous to lagoons in it origin (Fig. 1). For further limnological works, the morphometric data were calculated on the basis of isobathic map (Fig. 2) made by the staff of the Laboratory of Analytical Chemistry, Nagoya University (Table 1). The basin is flat and rather steeper in the southern part than in the northern where it was dammed with a narrow sand-dune isolating it from Lake Biwa. This shallow lake of marshy appearance is in senescent stage of succession, leaving the open surface in the south-western part where its maximum depth of 2.2m. was sounded.
The only inlet of the lake is a small stream which flows into Soné-numa in its south-western end. This stream (Fig. 3) receives several brooks which are fed by springs derived from the seepage water of the Usogawa River, of which the middle course is quite devoid of water and which runs into Lake Biwa at the north of Soné-numa. In the second section of the present paper, the drainage area of this river is discussed to a certain extent in relation to Soné-numa.

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The analysis of diatom shells has been made on cores of the bottom deposits of Soné-numa, a lagoon on the east coast of Lake Biwa. The results obtained from the core taken up in water depth of 2 m in the western part of the lake are described below. The core is 450 cm below the mud surface in its total length and may be classified into the eight layers with respect to diatom succession.
The first layer, 0-5 cm below the mud surface, is soft ooze containing abundant diatoms and is represented by the Fragilaria-Cyclotella-Cocconeis Association. The second layer, 5-15 cm, is represented by the Pinnulafia-Epithemia-GomPhonema Association, the components of which are rich in numbers of species but few in individuals as a whole. In the third layer, 15-55 cm, the diatoms are hardly found, while the fourth layer is made up by a small amount of diatoms, its flora being characterized by the Eunotia Association. In the fifth layer, 90-100 cm, diatoms are quite absent, as nearly similar to the third layer, but in the next sixth, 170-280 cm, a few diatoms occurs again showing the Eunotia Association as in the fifth layer. The seventh (280-370cm) and the eighth (370-450cm) layers contain abundant diatoms, the former being dominated by the Cocconeis-Amphora-Achnanthes Association and the latter by the Fragilaria-Amphora Association.
It is interesting to note that the lowest deposits (seventh and eighth layers) contain species which may be indicated as fossil or relic forms, namely, Amphora delphinea, Amphora ovalis var. libyca, Actinella brasiliensis, Gomphonema lingulatum, Cyclotella nipponica, Cymbella hybrida, Pinnularia lignitica and so on. They are not found in the layer upper than 280 cm of the core. This marked change between the upper and the lower parts of the core has been concerned in rather rapid modification of the environment in the lake during its history. It is also a striking fact that Melosira solida and Stephanodiscus carconensis, both plankton diatoms common to the main basin of Lake Biwa, have never occurred throughout the core.

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38 species of Rotatoria which were collected from a lagoon attaching to Lake Biwa (Soné-numa) were enlisted. The plankton samplings were carried horizontally either in the open water or among the colony of Trapa. Almost all the species collected from the open water were seen among the latter sample. Despite of comparatively low temperature of the water (15. 3°17°C), some austral or warm water rotifers were collected. Various forms of Keratella cochlearis which belong to the so-called “rnacracantha-typica-tecta series” occur red in the lagoon. In addition, 8 species of Protozoa are listed.

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