  A large number of stellar evolution models with [Fe/H] = -2.3 and -3.3 have
been calculated in order to determine the primordial $^7$Li abundance and to
test current stellar evolution models by a comparison to the extensive database
of Li abundances in extremely metal poor halo stars observed by Thorburn
(1994). Standard models do a good job of fitting the observed Li abundances in
stars hotter than 5600 K. They predict a primordial $^7$Li abundance of Log
N(Li) = 2.24\pm 0.03$. Models which include microscopic diffusion predict a
downward curvature in the $^7$Li destruction isochrones at hot temperatures
which is not present in the observations. Thus, the observations clearly rule
out models which include uninhibited microscopic diffusion of $^7$Li from the
surface of the star. The [Fe/H] = -2.3 stellar models which include both
diffusion and rotational mixing provide an excellent match to the observations.
Both the plateau stars and the heavily depleted cool stars are well fit by
these models. The rotational mixing leads to considerable $^7$Li depletion in
these models and the primordial $^7$Li abundance inferred from these models is
Log N(Li) = $3.08\pm 0.1$.
