Janus Capital Corp. of Denver said Thomas Marsico, manager of the $5.8-billion Janus Twenty Fund and the $1.7-billion Janus Growth & Income Fund, has left the firm. Janus, one of America's largest mutual fund groups, said in a statement that Marsico, 42, left because of "philosophical differences" and that his departure was voluntary and by mutual agreement. It did not say what Marsico, who had worked for the firm since 1986, plans to do next. Marsico could not be reached for comment. Industry analyst and financial advisor Eric Kobren of Wellesley, Mass., whose investment firm has about $85 million invested in a fund Marsico managed, said Marsico "wanted more management responsibility, and that was not to be, so he resigned." Scott Schoelzel, 38, manager of Janus Olympus Fund, will manage Janus Twenty. Dick Corkins, a Janus Mercury Fund assistant manager, will manage Janus Growth & Income.