Partially reduced derivatives of the novel quinones xestoquinone (1) and halenaquinone (2) have been isolated from an Adocia sp. sponge from Truk Lagoon. In addition, three derivatives of 1 and 2 which each possess an added l,l-dioxo-1,4-thiazine ring have been isolated. Structures for the latter compounds were confirmed by synthesis from 1 and 2. Cytotoxicity data are reported.