The founding members of 1980s metal band Megadeth have exchanged lawsuits, Billboard.biz reports. Bassist David Ellefson's action, filed July 12 in U.S. District Court for the Southern District of New York, alleges that co-founding guitarist David Mustaine breached their long-running partnership agreement. He claims Mustaine wrongfully took the lion's share of the band's income (estimated at more than $200 million since 1984) for himself and cut Ellefson out of the band's music publishing and merchandise revenues. Ellefson also says that Mustaine libeled him in an online posting. The bassist is seeking at least $18.5 million in damages. Mustaine's counterclaim, filed July 29 in California Superior Court in L.A., alleges that Ellefson on May 14 executed a settlement agreement in which he gave up his 20% interest in Megadeth. Mustaine maintains that the settlement -- which Ellefson alleges was signed under pressure and ultimately withdrawn -- released Mustaine from all claims. Mustaine's suit seeks damages to be determined. As previously reported, Megadeth will release a new studio album Sept. 14 via Sanctuary. The group's seven studio albums for Capitol/EMI were reissued last month by the label in expanded form.