  A molecular model of the $P_c(4457)$ and $P_c(4440)$ LHCb states is proposed.
The model relies on channels coupled by long range pion-exchange dynamics with
features that depend crucially on the novel addition of the
$\Lambda_c(2595)\bar D$ channel. A striking prediction of the model is the
unusual combination of quantum numbers $J^P(4457) = 1/2^+$ and $J^P(4440) =
3/2^-$. Unlike in other models, a simultaneous description of both states is
achieved without introducing additional short-range interactions. The model
also gives a natural explanation for the relative widths of the states. We show
that the usual molecular scenarios cannot explain the production rate of $P_c$
states in $\Lambda_b$ decays, and that this can be resolved by including
$\Lambda_c(2595)\bar D$ and related channels. Experimental tests and other
states are discussed in the conclusions.
