Sinae

... the outmoſt people to the eaſt, next the Sinus Magnus, and inclining to the ſouth, not to be blended with the Chineſe... Beyond the Sinae to the eaſt, and ſouth was a terra incognita... Iſ. Voſſius takes the Sinae to be the Siameſe; becauſe at this day the appellation Sinae is unknown aamong them; an argument which de Pinedo on Stephanus treats as trifling.

The sailing-course beyond the Ganges to the "country of the Sinae", as stated, would very nearly reach the Gulf of Tong-King.

Exactly which term, "Sinae" or "Serica", equates to the modern China is a bit muddled. Sinae could refer to eastern peninsular Southeast Asia or southern China or both whereas Serica could refer to northern China or Xinjiang and eastern Central Asia or both.