- A paper by McGurk on the evidence for citation marks in early texts speaks in passing of the diple:
The correct wedge-shaped diple is rare, but, once account is taken of this comparative rarity, its distribution in time and place can be described in the same way as that of the inset citation : it flourishes in the earlier uncial and half-uncial manuscripts (e.g. Paris lat. 2235, a 6th century Jerome, In Psalmos, CLA V 543) and is less usual later. A variety with a dot between the wedge is found at Tours (Paris lat. 1572, a late 8th century copy of the Concilium Ephesinum, CLA V 530) and at Echternach (so, Paris lat. 9538, an Augustine, De Trinitate, CLA V 588, and the Maihingen Gospels …. at Schloss Harburg). As with Greek manuscripts, the corrupt or debased diple is more and, on the whole, later than, the correct diple. The forms of its debasement are varied: that the many corrupt varieties, the commas, the s and r shapes, the wavy lines, derive from the correct arrowhead can be illustrated by many examples, none, perhaps, more convincing than the different forms of the diple used on [a referenced] page from the Codex Pisanus of Justinian’s Pandects, now at Florence in the Laurenziana (CLA III 295). (p.7)
Mc Gurk’s paper can be read, or downloaded [as a PDF] through Persee. Patrick McGurk, ‘Citation marks in early Latin manuscripts. With a list of citation marks in manuscripts earlier than A. D. 800 in English and Irish libraries)’, Scriptorium, Tome 15 n°1, 1961. pp. 3-13.
- Keith Houston gives a neat history of the diple in an article written for The New Yorker. ‘The Ancient Roots of Punctuation…’ was published on September 6th., 2013. and I’m so sure you’ll find it easily through your browser that I won’t add a link. 🙂