Servius on Virgil, Eclogue 6.72
…hoc autem Euphorionis continent carmina, quae Gallus transtulit in sermonem Latinum: unde est illud in fine, ubi Gallus loquitur “ibo et Chalcidico quae sunt mihi condita uersu carmina” Ecl. 10.50-1; nam Chalcis ciuitas est Euboeae, de qua fuerat Euphorion.
This [i.e. the origin of the Grynean wood] is treated in the poetry of Euphorion, which Gallus adapted into the Latin language. Hence that line at the end, where Gallus says: “I’ll go and [play] the songs I composed in Chalcidian verse”; for Chalcis is a city of Euboea, from which Euphorion came.