Elisha Grey would most likely say "who" rather than "what", as most Atlanteans of the Second Age would say -- and think.
The memory of their existence remains in the myths of Greece, Rome, and other cultures that absorbed the Atlantean diaspora at the end of the Third Age after the final destruction of the continent.
Part of the Second Age was technological innovation in all fields, including medicine, which forayed into genetic engineering in order to find solutions to chronic diseases, disabilities, and to increase lifespans. Hybridizing through cloning and gene splicing, these combinations of human and other animal genetic material survived. The result -- a race of human/animal conglomerates, some clearly showing whether their other genetic makeup was equine, leonine, avian, reptilian, or amphibious; and some such a mix that no species could be determined.
Living as a socially ostracized underclass in their own separate colony outside the large metropolitan capitol of Atlantis, along the eastern coast not far from the ferry docks that move between Atlantis and its split-off remnant of Poseidea, they work in Atlantis as laborers or service class employees. Some of them highly skilled and knowledgeable in their own right. They are a set of ears and eyes as observers that Elisha Grey trusts highly, and relies upon often. Chiron, the demiequine ironworker, woodworker, and tacit leader of the colony, is an ally in a number of the Chronicles. In the third story of The Casebook of Elisha Grey (I), "The Odalisques", Chiron and his partner, Phaedra, a human/reptilian hybrid, seek out Elisha Grey's help when their adoptive multimorph daughter disappears .
Image credit: "Eugène Ferdinand Victor Delacroix 036" by Eugène Delacroix - The Yorck Project: 10.000 Meisterwerke der Malerei. DVD-ROM, 2002. ISBN 3936122202. Distributed by DIRECTMEDIA Publishing GmbH.. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Eug%C3%A8ne_Ferdinand_Victor_Delacroix_036.jpg#/media/File:Eug%C3%A8ne_Ferdinand_Victor_Delacroix_036.jpg