Genus. _Histiogaster_, Berlese, 1883 515 _Histiogaster_ (_entomophagus_ ?) _spermaticus_, Trouessart, 1900 515 Genus. _Cheyletus_ 516 _Cheyletus mericourti_, Lab. 516 Family. _Sarcoptidæ_ (Itch Mites) 516 Sub-family. _Sarcoptinæ_ 518 Genus. _Sarcoptes_, Latreille 518 _Sarcoptes scabiei_, de Geer, 1778 518 _Sarcoptes minor_, Fürstenberg, 1861 520 Family. _Demodicidæ_ (Mites of the Hair-follicles) 522 Genus. _Demodex_, Owen 522 _Demodex folliculorum_, Simon, 1842 522 Order. _Pentastomida_ 523 Family. _Linguatulidæ_ 523 Genus. _Linguatula_, Fröhlich_ 524 _Linguatula rhinaria_, Pilger, 1802 524 Genus. _Porocephalus_ 526 _Porocephalus constrictus_, v. Siebold, 1852 526 _B._ INSECTA (_Hexapoda_) 529 CLASSIFICATION OF THE HEXAPODA.