It is most likely boisduval scale. photo here http://entnemdept.ufl.edu/creatures/...al_scale08.jpg
Back when I grew orchids I used to keep a bottle of 50% or 70% alcohol with a few drops of dawn dish detergent (as a sticker spreader) in it with a trigger sprayer (with the pickup tube cut to length to fit the alcohol bottle) on it just for killing these little suckers. After spraying the plant with this solution the buggers will be dead. The female scales will just flick right off after a couple of days. The alcohol will have killed the females hiding under the little domes that normally protect them from insecticides. No need to rinse the plants after applying this solution. I used it on orchids and nepenthes with no ill effects.