Paragate

On page Eighty one, is how to develop the Base of Boundless Consciousness.  This is not well described here, it is only to have no desire for the previous Base of Boundless Space, to concentrate on the consciousness.  Gunarata is of help:

Since the space taken as the object by the first formless jhana was boundless, the consciousness of that space also involves an aspect of boundlessness, and it is to this boundless consciousness that the aspirant for the next attainment adverts. He is not to attend to it merely as boundless, but as "boundless consciousness" or simply as "consciousness." He continues to cultivate this sign again and again until the consciousness belonging to the base of boundless consciousness arises in absorption taking as its object the boundless consciousness pertaining to the first immaterial state (Vism. 331-32; PP.360-61).

Also here is how to develop the third immaterial jhana, the Base of Nothingness.  Ready?  Back to Gunaratna: 


the meditator is to focus upon the present absence or non-existence of the consciousness belonging to the base of boundless space, adverting to it over and over thus: "There is not, there is not" or "void, void". When his efforts fructify there arises in absorption a consciousness belonging to the base of nothingness, with the non-existence of the consciousness of boundless space as its object. Whereas the second immaterial state relates to the consciousness of boundless space positively, by focusing upon the content of that consciousness and appropriating its boundlessness, the third immaterial state relates to it negatively, by excluding that consciousness from awareness and making the absence or present non-existence of that consciousness its object.