There's a ponderous pundit MacHugh Who wears goggles of ebony hue. As he mostly sees double To wear them why trouble? I can't see the Joe Miller. Can you?
In mourning for Sallust, Mulligan says. Whose mother is beastly dead.
Myles Crawford crammed the sheets into a sidepocket.
—That’ll be all right, he said. I’ll read the rest after. That’ll be all right.
Lenehan extended his hands in protest.
—But my riddle! he said. What opera is like a railwayline?
—Opera? Mr O’Madden Burke’s sphinx face reriddled.
Lenehan announced gladly:
—The Rose of Castile. See the wheeze? Rows of cast steel. Gee!
He poked Mr O’Madden Burke mildly in the spleen. Mr O’Madden Burke fell back with grace on his umbrella, feigning a gasp.
—Help! he sighed. I feel a strong weakness.
Lenehan, rising to tiptoe, fanned his face rapidly with the rustling tissues.
The professor, returning by way of the files, swept his hand across Stephen’s and Mr O’Madden Burke’s loose ties.
—Paris, past and present, he said. You look like communards.
—Like fellows who had blown up the Bastile, J. J. O’Molloy said in quiet mockery. Or was it you shot the lord lieutenant of Finland between you? You look as though you had done the deed. General Bobrikoff.
In this passage we find another reference to the Opera The Rose of Castile. In The Calumet of Peace, Myles Crawford quoted a line from it. I have an excerpt from the actual opera in post I did about that passage (source). Lenehan’s “riddle” is obviously a pun he came up with on the spot because Crawford had just been singing from the Opera.