3 new genera and 1 new subgenus are described: Plhudsonia n.gen. apparently related to Austrobrillia Freeman; Georthocladius Strenzke subgen. Atelopodella n.subgen.; Unniella n.gen. near Mesosmittia Brundin, but with genitalia resembling the Parakiefferiella group; and Platysmittia n.gen. related to Mesosmittia Brundin and Unniella n.gen. The genera Antillocladius Sasther, Lipurometriocnemus Sæther, Stilocladius Rossaro and Bryophaenocladius Thienemann are emended. A key to male imagines of Antillocladius is given. 10 new species are described: Plhudsonia partita, Antillocladius arcuatus, Antillocladius pluspilalus, Lipurometriocnemus vixlobatus, Psilometriocnemus cristatus, Atelopodella curticornus, Compterosmittia clavigera, Stilocladius clinopecten, Bryophaenocladius psilacrus, Unniella multivirga, and Platysmittia fimbriata. The description of Georthocladius (Atelopodella) curticornus is based on female, pupa and larva, while that of Psilometriocnemus cristatus and Stilocladius clinopecten includes male, female, pupa and larva; of Plhudsonia partita male and pupa, and the remaining ones are based on male imagines only. The South Carolina population of Diplocladius cultriger is compared with other Nearctic material and a male from Finse, Norway, and the possibility of non-conspecificity pointed out. Two unassociated pupae are described, one belonging to a genus near Brillia Kieffer, and one to a genus near Psilometriocnemus Sæther. One peculiar, unassociated larva is described apparently related to Acamptocladius Brundin. The orthoclad fauna treated show strong evidence of an ancestral generalized track between the southeastern states and the Antilles as well as evidence of common Gondwanean origin with some related genera from the subantarctic islands of New Zealand.