July 16 (Reuters) - Medical device maker Masimo Corp ( MASI )

on Tuesday said it has started litigation against

Politan Capital in a California federal court, seeking to force

the activist investor to correct "material misstatements and

omissions" in its proxy materials.

Masimo ( MASI ) is locked in a proxy contest with Politan, which has

long criticized the California-based company's board oversight

and expressed concerns about its purchase of Sound United.

Quentin Koffey-owned Politan owns nearly 9% stake in Masimo ( MASI )

and has been seeking two board seats in the company's

five-member board.

Masimo ( MASI ) has also postponed its annual shareholder meeting to

Sept. 19 from July 25 earlier, the company said in a statement.

Politan did not immediately respond to a Reuters request for

comment.