This species is known from subfossil remains that were recovered from deposits on the island of Rapa, Austral Islands.
The form apparently was similar yet smaller than the Buff-banded Rail (Gallirallus philippensis (L.)), like all now extinct Polynesian rails, also this form most likely was completely flightless. 
 J. D. Tennyson; Atholl Anderson: Bird, reptile and mammal remains from archaeological sites on Rapa Island. In: Atholl Anderson; Douglas J. Kennett: Taking the High Ground; The archaeology of Rapa, a fortified island in remote East Polynesia. In: Terra Australis 37. 105-114. Canberra, ANU E Press 2012
The Niue Rail was described in 2000 based on subfossil remains that had been found in deposits of the Anakuli Cave near the village of Hakupu on the the island of Niue.
These remains could be dated to an age of 5300 to 3600 years before present, thus predate human settlement on the island, however, there is, in my opinion, no doubt that the species nevertheless was extirpated by the first Polynesian settlers. 
The island of Niue is today inhabited by a subspecies of the Buff-banded Rail (Gallirallus philippensis ssp. goodsoni (Mathews)) that also inhabites the Samoan Islands nearby.
 David W. Steadman; Trevor H. Worthy; Atholl j. Anderson; Walter, Richard: New species and records of birds from prehistoric sites on Niue, southwest Pacific. Wilson Bulletin 112(2): 165–186. 2000
The New Ireland Rail was described in 2006, it was restricted to the island of New Ireland.
The species was among the larger members of its genus, probably reaching a size of about 30 cm, it was completely flightless. 
The New Ireland Rail very likely was closely related to the Pink-legged Rail (Gallirallus insignis (P. L. Sclater)) (see depiction below), a large, flightless rail from the neighboring island of New Britain.
 Jeremy J. Kirchman; David W. Steadman: Rails (Rallidae: Gallirallus) from prehistoric archaeological sites in Western Oceania. Zootaxa 1316: 1-31. 2006
This form is known from a drawing that was made on an island of the Vava’u group, probably ‘Uta Vava’u, during the so-called ‘Malaspina Expedition’, which visited the Pacific under the leadership of Alessandro Malaspina di Mulazzo, sometime between 1789 and 1794.
The brief description shows that the bird was bluish gray or ash gray in color, and that its plumage was less spotted or striped than most of the other species in the genus.
The species certainly died out a few years later. 
 Storrs L. Olson: Birds, including extinct species, encountered by the Malaspina Expedition on Vava’u, Tonga, in 1793. Archives of Natural History, 33(1): 42-52. 2006
Depiction made during the Malaspina Expedition between 1789 & 1794
The Tongatapu Rail is actually known only from the description of a single bird that was kept in the collection of Joseph Banks, a naturalist who took part in James Cook’s fisrt voyage from 1768 to 1771; this description can be found in John Latham’s ‘A general synopsis of birds’ from 1781-85.:
“The head in this variety is paler, and the streak over the eye grey: the hind part of the neck transversely striated brown and white: the middle of the back, and scapulars, white, with a very little mixture of brown on the first: wing coverts olive brown, transversely blotched with white; second quills white on the inner webs, on the outer olive brown; the greater quills olive brown, marked with large ferruginous spots; the first wholly white, the second white within: tail even with the end of the quills, barred olive brown and white: all the under parts white: bill and legs pale yellow brown.” 
The Tongatapu Rail mysteriously managed to somehow survive into the 18th century, its population, however, may already have been more or less crushed when the single specimen was taken in 1773 (?) during Cook’ second voyage, and the species died out completely shortly after.
There is a drawing made by georg Forster in 1774 (?), which is often referred to as showing this rail species, this, however, is false since this drawing was in fact made from a bird taken on the island of Nomuka and shows no other bird than the Tongan Buff-banded Rail (Gallirallus philippensis ssp. ecaudatus (J. F. Miller)) (see depiction below).
 John Latham: A general synopsis of birds. London: Printed for Benj. White 1781-1785  D. G. Medway: The Tongatapu rail Gallirallus hypoleucus (Finsch & Hartlaub, 1867) – an extinct species resurrected?. Notornis 57 (4): 199–203. 2010
Ha’afeva is a small, more or less flat coral island within the Ha’apai group in the middle of the Tongan archipelago.
Archaeological excavations on this island found, among other things, subfossil bones of an apparently flightless species of rail, which was exterminated by Polynesians a short time after the island was first settled.
The Haafeva Rail has not yet been scientifically described. 
 Jeremy J. Kirchman; David W. Steadman: Rails (Aves: Rallidae: Gallirallus) from prehistoric sites in the Kingdom of Tonga, including a description of a new species. Proceedings of the Biological Society of Washington 118(2): 465-477. 2005  David W. Steadman: Extinction and Biogeography of Tropical Pacific Birds. University of Chicago Press 2006
Wake Island is a small atoll in the Pacific Ocean, consisting of the three larger islands Peale, Wake and Wilkes Island and a few smaller islets. Wake Island has been a United States military base since the end of World War II. From a bird’s eye view, the viewer immediately sees the huge runway for airplanes.
In addition to numerous species of seabirds, the atoll was once home to an endemic species of rail, which apparently only inhabited the two islands of Wake and Wilkes, but did not occur on Peale Island.
The Wake Rail was described in 1903 by Lionel Walter Rothschild under the name Hypotaenidia wakensis. Later, in 1923, the species was mentioned a second time. From July 27 to August 5, 1923, the “Tanager Expedition” stayed on Wake Island to study the native flora and fauna. Frank Alexander Wetmore, a well-known ornithologist and participant of this expedition, wrote a few lines about the Wake Rail during this time:
“These birds seem very sedentary. Those that I take on sandy areas where there is only scattered areas of shade, are very worn and pale color above, those from certain sections where there are extensive dead-falls have the wing feathers worn and abraded, apparently from their use in climbing about . This is true though more suitable areas where conditions are less severe may be found near at hand. The wing claw in this species is very large and strong.“
During World War II, the atoll was occupied by Japanese troops, which, in the course of the war, were cut off from their supplies. So they had to take care of themselves, and so the tasty, easy-to-capture, because completely flightless Wake Rails came in handy. The soldiers’ appetites, however, were very large, too large for the small population of the rail species.
After the end of World War II, the Wake Rail no longer existed.
 Dieter Luther: Die ausgestorbenen Vögel der Welt. Westarp Wissenschaften 1986  Errol Fuller: Extinct Birds. Penguin Books (England) 1987  Barry Taylor, Ber van Perlo: Rails: A Guide to the Rails, Crakes, Gallinules and Coots of the World. Yale University Press 1998  David W. Steadman: Extinction and Biogeography of Tropical Pacific Birds. University of Chicago Press 2006