  From a sample of $2722 \pm 78$ $\Lambda_c^+$ decaying to the $pK^-\pi^+$
final state, we have observed, in the hadroproduction experiment E791 at
Fermilab, $143 \pm 20$ $\Sigma_c^0$ and $122 \pm 18$ $\Sigma_c^{++}$ through
their decays to $\Lambda_c^+ \pi^{\pm}$. The mass difference $M(\Sigma_c^0) -
M(\Lambda_c^+$) is measured to be $(167.38\pm 0.29\pm 0.15) {MeV}$; for
$M(\Sigma_c^{++}) - M(\Lambda_c^+)$, we find $(167.76\pm 0.29\pm0.15) {MeV}$.
The rate of $\Lambda_c^+$ production from decays of the $\Sigma_c$ triplet is
$(22\pm 2\pm 3) {%}$ of the total $\Lambda_c^+$ production assuming equal rate
of production from all three, as measured for $\Sigma_c^0$ and $\Sigma_c^{++}$.
We do not observe a statistically significant $\Sigma_c$ baryon-antibaryon
production asymmetry. The $x_F$ and $p_t^2$ spectra of $\Lambda_c^+$ from
$\Sigma_c$ decays are observed to be similar to those for all $\Lambda_c^+$'s
produced.
