*G. Arthropoda* (Jointed-limbed Animals) 483 _A._ ARACHNOIDEA (Spiders, Mites, etc.) 483 Order. _Acarina_ (Mites) 484 Family. _Trombidiidæ_ (Running Mites) 485 Genus. _Trombidium_, Latreille (and Leptus) 485 _Leptus autumnalis,_ Shaw, 1790 485 _Trombidium tlalsahuate_, Lemaire, 1867 486 _Akamushi_ or _Kedani_ 487 Family. _Tetranychidæ_ (Spinning Mites) 488 Genus. _Tetranychus_, Dufour 488 _Tetranychus molestissimus_, Weyenbergh, 1886 488 _Tetranychus telarius_, L., 1758, var. russeolus, Koch 488 Family. _Tarsonemidæ_ 488 Genus. _Pediculoides_ 489 _Pediculoides ventricosus_, Newport, 1850 489 Genus. _Nephrophages_ 490 _Nephrophages sanguinarius_, Miyake and Scriba, 1893 490 Family. _Eupodidæ_ 491 Genus. _Tydeus,_ Koch 491 _Tydeus molestus_, Moniez, 1889 491 Family. _Gamasidæ_ (Coleopterous or Insect Mites) 491 Genus. _Dermanyssus_, Dugès 492 _Dermanyssus gallinæ_, de Geer, 1778 492 _Dermanyssus hirundinis_, Hermann, 1804 492 Genus. _Holothyrus_ 493 _Holothyrus coccinella_, Gervais, 1842 493 Family. _Ixodidæ_ (Ticks) 493 Classification of _Ixodidæ_ 496 Synopsis of Genera 496 Genus. _Ixodes_, Latreille 497 _Ixodes reduvius,_ L., 1758 497 _Ixodes holocyclus_, Neumann, 1899 499 _Ixodes hexagonus_, Leach, 1815 500 Genus. _Amblyomma_, Koch 500 _Amblyomma cayennense_, Koch, 1844 500 _Amblyomma americana_, Linnæus 501 _Amblyomma maculatum_, Koch 501 Genus. _Hyalomma_, Koch 501 _Hyalomma ægyptium_, L., 1758 501 Genus. _Hæmaphysalis_, Koch 502