Eikadistes , I had never seen that but I am definitely intrigued.
So, the form of that is:
ΣTOIXEIΩΣEIΣ ΔΩΔEKA
(or in upper & lower case, for comparison)
Στοιχειώδεις δώδεκα.
I was curious to see how the other sets of books were listed in Diogenes ' Book 10:
Περὶ φύσεως ἑπτὰ καὶ τριάκοντα.
On Nature (in) 37 (books)
Ἐπιστολικὰ περὶ Ἐμπεδοκλέους εἴκοσι καὶ δύο.
Letters concerning Empedocles (in) 22 (books)
Πρὸς τοὺς σοφιστὰς ἐννέα.
Against the Sophists (in) nine (books)
Πρὸς τοὺς ἰατροὺς τρία.
Against the Physicians (in) three (books)
There were others but those only used numerals. But these three here all use the number directly after the title and are translated, with no fanfare, as Title (in) X# (books).
I do notice that the form in Diogenes 10.44 is ταῖς Δώδεκα στοιχειώσεσί with the number preceding the "elements/principles." However, in looking at them placement of other numbers in relation to the noun they're modifying, some are before, some after. The placement of Δώδεκα between the definite article and στοιχειώσεσί leads me to interpret ταῖς Δώδεκα στοιχειώσεσί as "in The 12 Principles/ Elements." I'm not saying I couldn't be persuaded otherwise, but that's my current understanding.
