Two new species of the genus Petrobia Murray, 1877, subgenus Petrobia, are described from Iran: P. (P.) norbakhshi sp. nov. from wild garlic and P. (P.) hordei sp. nov. from barley. The former species is described from females, and the latter is from females, deutonymphs, protonymphs and larvae. Petrobia (P.) latens (Müller, 1776) is also re-described based on females, deutonymphs and protonymphs. Leg chaetotaxy is provided for each species, and is shown to be reasonably consistent within species of Petrobia (Petrobia). The subgenera of Petrobia—Petrobia, Mesotetranychus and Tetranychina—are redefined, resulting in some species being re-classified in different subgenera. A key to species of the subgenus Petrobia is given.