Here is the Latin text
where the place-name is first mentioned:
[This comes directly after a description of the way from Mediterranean to Atlantic, Pillars of Hercules, Gades (modern Cadiz) etc.]
et prominentis hic iugi surgit caput,Oestrymnin
istud dixit aevum antiquius, 90
molesque celsa saxei fastigii
tota in tepentem maxime vergis notum.
sub huius autem prominentis vertice
sinus dehiscit incolis Oestrymnicus,
in quo insulae sese exerunt Oestrymnides, 95
laxe iacentes et metallo divites
stanni atque plumbi. multa vis hic gentis est,
superbus animus, efficax solertia,
negotiandi cura iugis omnibus,
netisque cumbis turbidum late fretum 100
et beluosi gurgitem Oceani secant.
non hi carinas quippe pinu texere
et acere norunt, non abiete, ut usus est,
curvant faselos, sed rei ad miraculum
navigia iunctis semper aptant pellibus 105
corioque vastum saepe percurrunt salum.
Translation from George Smith, The Cassiterides
Here rises the head of the promontory in olden times named Oestrymnin (which this translation identifies as Cape Finisterre) and below the like named bay and isles; wide they stretch and are rich in metals, tin and lead. There a numerous race of men dwell, endowed with spirit and no slight industry, busied all in the cares of trade alone. They navigate the sea on their barks, built not of pines or oak, but wondrous! made of skins or leather.
ast hinc duobus in sacram, sic insulam
dixere prisci, solibus cursus rati est.
haec inter undas multam caespitem iacet,
eamque late gens Hiernorum colit. 110
propinqua rursus insula Albionum patet.
Two days thence is the voyage to the Holy Island, once so called, which lies expanded on the sea, the dwelling of the Hibernian [Irish] race; at hand lies the isle of Albion.
The poem goes on to say that "of yore the trading voyages from Tartassus reached to the Oestrymninides: but the Carthaginians and their colonies near the pillars of Hercules navigated in this sea, which Hamlico, by his own account, was upon during four months."