  We study the matrix quantum mechanics of two free hermitian $N\times N$
matrices subject to a singlet constraint in the microcanonical ensemble. This
is the simplest example of a theory that at large $N$ has a
confinement/deconfinement transition. In the microcanonical ensemble, it also
exhibits partial confinement with a Hagedorn density of states. We argue that
the entropy of these configurations, calculated by a counting of states based
on the fact that Young diagrams are dominated by Young diagrams that have the
VKLS shape. When the shape gets to the maximal depth allowed for a Young
diagram of $SU(N)$, namely $N$, we argue that the system stops exhibiting the
Hagedorn behavior. The number of boxes (energy) at the transition is $N^2/4$,
independent of the charge of the state.
