Süsswasserbewohnende halacariden und ihre einordnung in das system der halacaroidea (acari). - The fresh-water halacarid genera are .described and their relationship to marine genera discussed. A new genus, Ropohalacarus, is established and diagnosed. Astacopsiphagus, Lobohalacarus and Porohalacarus are related to the Halacarinae; the limnohalacarins, Porolohmanel/a and Ropohalacarus, related to the LohmannelIinae. Caspihalacarus and Troglohalacarus are extremely similar to species of the marine genus Halacarelus. Transitional stages are to be expected. Pseudosoldanellonyx and Stygohalacarus are hardly distinguishable from Soldanellonyx; they should be considered ·as synonymous with Soldanellonyx.