  The specific heat of polycrystalline Mg$^{11}$B$_{2}$ has been measured with
high resolution ac calorimetry from 5 to 45 K at constant magnetic fields. The
excess specific heat above T$_{c}$ is discussed in terms of Gaussian
fluctuations and suggests that Mg$^{11}$B$_{2}$ is a bulk superconductor with
Ginzburg-Landau coherence length $\xi_{0}=26$ \AA . The transition-width
broadening in field is treated in terms of lowest-Landau-level (LLL)
fluctuations. That analysis requires that $\xi_{0}=20$ \AA . The underestimate
of the coherence length in field, along with deviations from 3D LLL
predictions, suggest that there is an influence from the anisotropy of B$_{c2}$
between the c-axis and the a-b plane.
