Study of orbitolines in many Cretaceous localities of northern Spain shows that these foraminifera flourished in very diverse marine environments, at shallow depths but beyond the turbulent littoral zone. Many variations may exist within a single species in a given deposit. Some species were more adept than others at agglutinating detritus available nearby. Large flat forms developed preferably on bottoms with abundant terrigenous material. Criteria for defining species should be found by comparing certain measurable characteristics.