  We study the maximal compact subgroup K(E_9) of the affine Lie group E_9(9)
and its on-shell realization as an R symmetry of maximal N=16 supergravity in
two dimensions. We first give a rigorous definition of the group K(E_9), which
lives on the double cover of the spectral parameter plane, and show that the
infinitesimal action of K(E_9) on the chiral components of the bosons and the
fermions is determined in terms of an expansion of the Lie algebra of K(E_9)
about the two branch points of this cover; this implies in particular that the
fermions of N=16 supergravity transform in a spinor representation of K(E_9).
The fermionic equations of motion can be fitted into the lowest components of a
single K(E_9) covariant `Dirac equation', with the linear system of N=16
supergravity as the gauge connection. These results suggest the existence of an
`off-shell' realization of K(E_9) in terms of an infinite component spinor
representation. We conclude with some coments on `generalized holonomies' of M
theory.
