What is the test for dismissing a complaint for failure to state a claim?

It is "the accepted rule that a complaint should not be dismissed for failure to state a claim unless it appears beyond doubt that the plaintiff can prove no set of facts in support of his claim which would entitle him to relief." Conley v. Gibson, 355 U.S. 41, 45-46, 78 S.Ct. 99, 102, 2 L.Ed.2d 80 (1957) (footnote omitted). It is not clear at this juncture that plaintiffs cannot present such proof. A ruling on the legal adequacy of their claim should await further development of the facts. We express no opinion as to the merits of appellants' contentions or the ultimate disposition to be made by the district court.