There is no comment on etymology or type species (Tharyx acutus & T. similis named). As 'acutus' is masculine and 'similis' is unchanged between masculine and feminine, then Tharyx is masculine, because Hartman catalogue made the type species Tharyx acutus, presumably on page priority.
Webster, Henry E. and Benedict, James E. (1887). The Annelida Chaetopoda, from Eastport, Maine. U.S. Commission of Fish & Fisheries. Report of the United States Commissioner of Fisheries. 1885. part 13, II. appendix to report of commissioner, D.22. :707-758, including pls. 1-8. available online athttp://biodiversitylibrary.org/page/15839855