A comparison of the faunal characteristics of two foraminifera Assemblages from the Rosario Formation in 9aja California sugQests the following general criteria wnich may prove to be useful in the intorpretation of Upper Cretaceous paleoenvironments: 1) specific group of arenAceous foraminifers characterize relatively deAp-water assemblages, 2) arenaceous foraminifer9 constitute the greatest percentage of tests in relatively deep-wnter assemblages, 3) specimens of Bulimina are not abundant in relatively shallow-wate assemblages, and 4) jttached foraminifers are most abundant in relatively shallow-wter faunas. Sixty species and subspecies of benthonic fornminifera sre recorded from the two faunules; only six worR common to both faunules.
