From Thomas Edwards' The Canons of Criticism, printed by C. Bathurst (1765) in London, in a font that (as you can see) has long-S and c-t ligatures:
The text centered in this image says:
of Nat. Bailey, φιλολογⒼ: A horny induration of
What on earth is that "circled G" glyph that I've rendered "Ⓖ" above? I suppose that it was meant to represent -ος, as in φιλολογος "philologist"; my curiosity is entirely about the typographical aspect.
Was this glyph (whatever it is) correctly used, here? Is it some Greek ligature I haven't seen before?
(More likely) Was this just a printer's error? I could imagine the sequence of handwritten characters "ος" being misinterpreted as "circle, G." But then, how did the printer come to possess a piece of type for this "Ⓖ" glyph already? What is the intended use for this glyph, and where else would I find it used?
Except for the circle, it looks a bit like an "et" ligature (ampersand); is that relevant?