#Music service, just six months after launching it, according to AllThingsD. The #Music mobile app was an iOS hit when it first launched, but download levels are now "abysmal," according to AllThingsD's sources. Although Twitter has continued to add features to the music discovery service, which relies on partners such as Rdio and Spotify to actually play music, its fate may have been sealed by the departure of project head Kevin Thau, who left Twitter shortly after #Music was launched to join Twitter co-founder Biz Stone's Jelly startup. According to AllThingsD, "that left the app, a product some have said felt half-baked, in the wind." Twitter has, apparently, already decided that #Music may not be a great source for direct revenue. In the company's recent IPO filing, Twitter, which makes "the substantial majority" of its revenue from advertising, declared that "we do not currently place, or currently plan to place, ads on #Music."