African Chlorocyphidae have hitherto been regarded as fluvial species, inhabiting streams or rivers in shaded surroundings. Populations of Platycypha caligata have recently been found on Lake Malawi adapted to lacustrine shade conditions. Morphological differences in the adult from typical material are slight but definite. A specimen collected from the lake shore nineteen years previously also shows the peculiarities of this lacustrine material, adding confirmation. Both subspecies of caligata are examined for comparisons. The new lake form is named P. c. caligata morph lacus nov. An additional note is that the original reference normally quoted as 1928 for Fraser’s genus Chlorocypha should be amended to 1934. A gazetteer is included.