I'd sketched the serial case, whereas I think I meant the parallel one where the decomposition would come out as:

Proc 0:

nodes = op2.Set([0,2,4,4])
elems = op2.Set([0,1,2,2])

And similarly on Proc 1, with appropriate Maps.  Essentially this is the mpi mass2d example mesh description.

So it's possible that the plan is correct.