This seems to be a continuation of the references to Dante begun in lines 11-12. The suggestion seems to be that "the condition of the hollow men is that of the lost souls in Hell. They are the inhabitants of
'death's dream kingdom' gathered at the last meeting place beside a
'tumid river'.
In Dante this corresponds to the scene beside the River Acheron (in the INFERNO) where the spirits of the damned wait to be ferried across to Hell."