  We undertake a statistical analysis of the radial abundance distributions in
the Galactic disk within a theoretical framework for Galactic chemical
evolution which incorporates the influence of spiral arms. 1) The mean mass of
oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated
within spiral arms) is $\sim$0.27 M$_{\odot}$; 2) the mean mass of iron ejected
by `tardy' Type Ia SNe (SNeIa; progenitors of whom are older/longer-lived stars
with ages $\simgt$100 Myr and up to several Gyr, which do not concentrate
within spiral arms) is $\sim$0.58 M$_{\odot}$; 3) the upper mass of iron
ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars
with ages $\simlt$100 Myr, which are concentrated within spiral arms) is
$\leq$0.23 M$_{\odot}$ per event; 4) the corresponding mean mass of iron
produced by CC SNe is $\leq$0.04 M$_{\odot}$ per event; (v) short-lived SNe
(core-collapse or prompt SNeIa) supply $\sim$85% of the Galactic disk's iron.
  The inferred low mean mass of oxygen ejected per CC SNe event implies a low
upper mass limit for the corresponding progenitors of $\sim$23 M$_{\odot}$,
otherwise the Galactic disk would be overabundant in oxygen.
  The low mean mass of iron ejected by prompt SNeIa, relative to the mass
produced by tardy SNeIa ($\sim$2.5 times lower), prejudices the idea that both
sub-populations of SNeIa have the same physical nature. We suggest that,
perhaps, prompt SNeIa are more akin to CC SNe, and discuss the implications of
such a suggestion.
