  We report measurements of the temperature dependence of both in-plane and
out-of-plane penetration depths ($\lambda_a$ and $\lambda_c$ respectively) in
2\textit{H}-NbSe$_2$. Measurements were made with a radio-frequency tunnel
diode oscillator circuit at temperatures down to 100 mK. Analysis of the
anisotropic superfluid density shows that a reduced energy gap is located on
one or more of the quasi-two-dimensional Nb Fermi surface sheets rather than on
the Se sheet, in contrast to some previous reports. This result suggests that
the gap structure is not simply related to the weak electron-phonon coupling on
the Se sheet and is therefore important for microscopic models of anisotropic
superconductivity in this compound.
