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Summary.

The morphology of the freshwater medusa, Limnocnida rhodesiœ Boulenger, obtained from new sites in the Zambesi and Limpopo river-systems, is described and illustrated by photographs (Pl. I.).

The new sites for L. rhodesiœ are the Prince Edward Dam on the Hunyani River, near Salisbury, the Hartebeestpoort Dam on the Crocodile River, near Pretoria, and the Bezuidenhout Valley in Johannesburg.

The range of dimensions of L. rhodesiœ is extended, the present specimens being larger than those previously described.

The specimens of L. rhodesiœ examined from the new localities were all females in active egg-production. Manubrial bud-formation was seen in only a few specimens.

A species of Trichodina occurred in small numbers on the external surface and tentacles of L. rhodesiœ from the new localities cited.

Some ecological notes on Limnocnida are given.

The present geographical distribution of the genus Limnocnida is discussed and the continued southward range of distribution in Africa from Lake Victoria Nyanza to Johannesburg is detailed. Similarly, the distribution of the known species of Limnocnida is given, L. tanganicœ, the Central African form, being replaced by L. rhodesiœ in Rhodesia and the Transvaal, and by L. indica in India.

The possible significance of the present-day geographical distribution of Limnocnida in relation to former geological conditions on the earth's surface is discussed.