The English specimens listed below were captured on wild examples of the brown rat by the author, and those from Scotland by Waterston. Several of these mites have already been recorded by Dr. A. C. Oudemans and other authors as occurring on this host. Only three of the species (Laelaps echidninus, Notoedres muris and Myobia ensifera) can be regarded with certainty as being practically restricted to Mus norvegicus, but this is possibly also the case with Haemogamasus oudemansi, which so far has only been found on this host. The other species are frequently found on other mammals or in their nests, especially in that of the mole (see Oudemans, Acarologisches aus Maulwurfsnestern, Arch. Naturg. Berlin, 1913).