This is a interesting Shape 3 Delphis plate as it is made out of black clay and the underneath of the plate is glazed in the sea crest glaze.
 
Plates like this were only produced for a very short time, probably because the higher firing temperature for the black clay affected the delphis glazes.
 
There is no paintress mark but it looks to be painted by Margaret Anderson which would date it to 1966-7.
 
The plate is in excellet condition with no chips, cracks or restoration.