In the Eumenides, the tragedy by Aeschylus about the Erinyes and Orestes, the Erinyes are described as dark, not quite women, not quite Gorgons (Medusas), featherless, with rheumy eyes and partial to blood. Source: "The Appearance of Aeschylus' Erinyes," by P. G. Maxwell-Stuart. Greece & Rome, Vol. 20, No. 1 (Apr., 1973), pp. 81-84.
Jane E. Harrison (September 9, 1850 - April 5, 1928) says the Erinyes at Delphi and elsewhere were ancestral ghosts, who later became "detached ministers of divine vengeance". The Erinyes are the dark aspect of the benevolent Eumenides -- the angry ghosts. [Source: Delphika.-(A) The Erinyes. (B) The Omphalos," by Jane E. Harrison. The Journal of Hellenic Studies, Vol. 19, (1899), pp. 205-251.] It is also claimed that Eumenides is a euphemism for the Erinyes.