Monotypic prehistoric arachnid genera

Brontoscorpio is an extinct genus of possible scorpion that lived in the Early Devonian. Remains of the only known species, Brontoscorpio anglicus, were discovered in the St. Maughan's Formation, Lochkovian-aged (previously also considered as late Silurian) sandstone from Trimpley, Worcestershire.

Plesiosiro is an extinct arachnid genus known exclusively from nine specimens from the Upper Carboniferous of Coseley, West Midlands, United Kingdom. The genus is monotypic, represented only by the species Plesiosiro madeleyi described by Reginald Innes Pocock in his important 1911 monograph on British Carboniferous arachnids. It is the only known member of the order Haptopoda.

Permarachne is an extinct genus of arachnids containing the single species Permarachne novokshonovi from the Permian (Kungurian) of Russia, found in the Koshelevka Formation near the town of Suksun in Perm Krai. It is closely related to modern spiders but unlike them, it has a long thin tail, similar to its relative Attercopus, it is known from the mostly complete holotype PIN 4909/12. It is about 1 cm in size. It initially was thought to be a spider, but is now thought to form a clade with at least its close relative Attercopus, forming the grouping Uraraneida.