  We report a numerical study, covering a wide range of packing fraction $\phi$
and temperature $T$, for a system of particles interacting via a square well
potential supplemented by an additional constraint on the maximum number
$n_{\rm max}$ of bonded interactions. We show that when $n_{\rm max}<6$, the
liquid-gas coexistence region shrinks, giving access to regions of low $\phi$
where dynamics can be followed down to low $T$ without an intervening phase
separation. We characterize these arrested states at low densities (gel states)
in terms of structure and dynamical slowing down, pointing out features which
are very different from the standard glassy states observed at high $\phi$
values.
