Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Myrtōus, a, um, adj., = Μυρτῶος, Myrtoan: Myrtoum mare, the Myrtoan Sea, a part of the Ægean Sea, between Crete, the Peloponnesus, and Eubœa, which derives its name from the island of Myrtos, Plin. 4, 11, 18, § 51; Hor. C. 1, 1, 14: so, pelagus, Mel. 2, 3, 3; 2, 7, 10: aqua, Ov. Ib. 372.