van Thiel:
Σ 604 τερπόμενοι· [μετὰ δέ ϲφιν ἐμέλπετο θεῖοϲ ἀοιδὸϲ
Σ 605 φορμίζων,] δοιὼ δὲ κυβιϲτητῆρε κατ’ αὐτοὺϲ
West:
Σ 604/605 τερπόμενοι· δοιὼ δὲ κυβιστητῆρε κατ’ αὐτούς
What is the story with Wolf’s insertion at S604/605? West has a description (in Latin) that I don’t entirely understand.
I don’t have either of these editions before me right now, but I would assume that the words in question are considered spurious because they’re weakly attested in the mss. (i.e., they appear in only one or just a few manuscripts). There are many whole lines in the Homeric poems like this, but here we have a string of words that are believed to have been inserted in the middle of a line so as to form two metrically compliant lines. Maybe they’re an advertisement for the aoidos.
Both van Thiel and West seem to be rejecting these words. Wolf’s edition provides the standard line-numbering, so an editor who doesn’t think they’re genuine has to either bracket them (van Thiel) or leave them out completely but account for the gap (West). They can be dropped without disturbing the meter, and the pronoun αυτους would seem odd if separated by the words in question from ομιλος in the immediately preceding line.
I can’t check right now, but these words may be indentical to words in the Phaeacian episode of the Odyssey, and hence thought to be copied from there. The aoidos Demodocus does sing some songs as part of the evening’s entertainment in that episode.
The same three lines occur at Od. 4.18-20. Telemachus arrives at Nestor’s palace and finds a wedding in progress. It looks as if the editors think someone interpolated the extra words from the Odyssey passage in the Iliad passage, which describes a festival portrayed on Achilles’ shield.
As previously mentioned, if the words are weakly attested in the Iliad passage, the likelihood is that they were interpolated there by someone familiar with the Odyssey passage. Or at least that would be the assumption.
A quick glance at West’s Studies in the Text and Trasmission of the Iliad:
The words are not weakly attested, they are unattested. Wolf “restored” them, following the Odyssey passage, because Athenaeus thought that Aristarchus had removed them. The text in Athenaeus is actually part of an argument that the passage in the Odyssey is interpolated from the Iliad. The story is somewhat complex, so I’m not going to refer it all.
The standard line numbering we still use derives from Wolf, in West’s words “giving the insertion an air of authority it doesn’t merit”.