抄録
The small daphnid inhabiting the two alpine lakes, Mikuri-ga-iké and Midoriga-iké, which lie at an elevation of 2405m. and 2430m. respectively on Mt. Tatéyama, is identical with Daphnia ambigua SCOURFIELD, by the characteristics of the post-abdominal claws and the male antennules as well as in having a short shellspine. When the writers visited those lakes on October 6th, 1960, both the populations of that species yielded a great number of the males and the females carrying ephippial eggs. In Mikuri-ga-iké, the deeper one of the two lakes and having 14.5m. in greatest depth, most individuals were seen at the layer 4m. deep, where the temperature of water was 10.3°C. Dinobryon was found in the digestive truct of Daphnia in both the lakes, although it was uncertain whether Daphnia was able to use this alga as food or not. It is noticeable that both the populations of Daphnia were markedly red-coloured, probably due to the increase of haemoglobin. Red colour was remarkable in the population of Lake Midori-ga-iké, a. shallow body of humose water east of Lake Mikuri-ga-iké. Some limnological characteristics of these two alpine lakes are discussed in showing the nature of the habitats of Daphnia ambigua.
