A new staurosporine analog, 4'-N-demethyl-l1 -hydroxystaurosporine (l), has been isolated by cytotoxicity-guided fractionation of an organic extract of the prosobranch mollusk Coriocellu nigru. The known staurosporine derivative 3,lldihydroxystaurosporine (2) was also isolated from this extract. Concurrent investigations of Coriocellu hibyae resulted in the isolation of two known compounds, lamellarins C (3) and U (4). The structures of 1, 2, 3 and 4 were elucidated by spectroscopic methods and the compounds were evaluated for cytotoxicity against 10 human tumor cell lines. Compounds 1 and 2 demonstrated potent cytotoxic activity with ICso's ranging from approximately 2 to 66 ng/mL.