  By postulating that the majority of the mass and angular momentum of a disc
galaxy is confined to the disc with a lognormal surface density distribution,
and that galactic discs are substantially, if not fully, self-gravitating, it
may be shown that the resultant rotation curves (RCs) display a good overall
fit to observational data for a wide range of galaxy types. With this
hypothesis, the total angular momentum $J$, and total energy |$E$| of 38 disc
galaxies was computed and plotted against the derived disc masses, with best
fit slopes for $J$ of $1.683\pm0.018$ and |$E$| of $1.643\pm0.038$, and a
universal disc spin parameter $\lambda=0.423\pm0.014$. Using the disc
parameters $V_{max}$ and $R_{max}$ as surrogates for the virial velocity and
radius, a virial mass estimator $M_{disc}\propto{}R_{max}V_{max}^2$ was
generated, with a log-log slope of $1.024\pm0.014$ for the 38 galaxies, and a
proportionality constant
$\lambda^*=1.47\pm0.20\times10^5M_\odot{}kpc^{-1}km^{-2}s^2$. This relationship
has less scatter than $M_\odot\propto{}V^\alpha$, and may provide an
alternative to the Tully-Fisher relation in determining virial disc masses.
