Observations sur les Pergamasus IV. Un essai de coordination de la taxonomie et de la chorologie du sous-genre Pergamasus s. s. (Acariens Anactinotriches, Parasitidae). The reader is informed of the starting hypothesis. Some considerations about the systematical practice, mostly that which concerns the taxa of lower categories, are recalled: usefulness of the biogeography (and reversely), semaphoronts more or less expressive of the phyletic radiations within those lower categories, phyletic status of somatotypical elements ... The subgenus Pergamasus, a bipolar taxon, exhibits its larger systematic diversification and its maximum ecological success in the northern hemisphere; in Europe, several branches are nowadays neo- or paleoendemic. This state of things could have resulted, historically, from a rivalry with other bipolar strains of Gamasina, such as the Rhodacaridae, etc., the situation of which is symmetrical in the southern hemisphere (number of species, ecological success).