The Rapa Kingfisher is yet a hypothetical species that I like to erect based on an account from the 1920s. 
This account speaks about the color symbolism of Rapan feather cloaks and says that royal cloaks incorporated dark blue feathers from a bird named “kotokoto”, which was supposed to have been a kingfisher, apparently most likely the Tuamotu Kingfisher (Todiramphus gertrudae Murphy) [but named Halcyon gambieri in the paper ].
I personally think that this is rather unlikely, if the feathers came from any kind of imported kingfisher species, as the paper  suggests, then probably not from birds from Mangareva (which were already almost extinct at that time) but even more unlikely from birds from the Niau atoll, which is located far, far away from the island of Rapa. They may, however, have come from the far more closely situated Cook Islands, which harbors more than one endemic kingfisher forms. But there may very well once have been an endemic kingfisher species on the island of Rapa as well, because why not?!
 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
Guadalcanal Little Kingfisher (Ceyx pusillus ssp. aolae)
The Guadalcanal Little Kingfisher is one of the nine subspecies of the Little Kingfisher (Ceyx pusillaTemminck), a species that occurs from Australia to parts of melanesia; it is known only from the type specimen that was collected on the island of Guadalcanal, eastern Solomon Islands.
The single known specimen is very similar to Richard’s Little Kingfisher (Ceyx pusillus ssp. richardsi Tristram) (see depiction) from the central Solomon Islands, it differs from that subspecies by its incomplete pectoral band and by its white, blue-tipped undertail coverts. 
The Guadalcanal Little Kingfisher is often thought to be extinct, this, however, is not entirely certain.
The Sangihe Dwarf Kingfisher was described in 1898; it was for a long time treated as a subspecies of the Sulawesi Dwarf Kingfisher (Ceyx fallax (Schlegel)) (see depiction), a small, about 12 cm large, colorful bird that itself inhabits the island of Sulawesi, Indonesia. It is now considered a full species again.
The Sangihe Dwarf Kingfisher, as its name implies, is, or maybe was, restricted to the island of Sangihe Besar in the Sangihe Islands off northern Sulawesi.
The species differed from the Sulawesi Dwarf Kingfisher mainly by its slightly larger size as well as by its crown in which the blue bars are larger and more lustrous, by its blackish instead of lilac superciliary region and by its more lilac rump and wings. 
The Sangihe Dwarf Kingfisher was last seen in 1997, and given the fact that its home island is now almost completely deforested, the chances for any population to have survived until today are very low – it is possibly extinct.
This species, if indeed it is one, is known exclusively by a single specimen which is believed to have been collected in 1887 on the island of Miyakojima in the Ryukyu Islands, Japan.
The sole specimen is very similar to the Guam Kingfisher (Todiramphus cinnamominus (Swainson)) (see photo), itself being extinct in the wild and currently only surviving in captivity, but differs in lacking the black nape band and in having reddish instead of blackish feet. The color of its beak is not known since the specimen is lacking its rhamphotheca.
The Ryukyu Kingfisher is not accepted as a valid taxon by all ornithologists.
The Madagascar Pygmy Kingfisher, locally known as Tsakoko manga, is a 12 to 13 cm large, typical kingfisher species that inhabits large parts of Madagascar.
The form discussed here is known from only a single specimen which was collected around 1970 in the Zombotse Forest near the city of Sakaraha in the Sakaraha District, Toliary Province in the arid southwest of Madagascar, and which differs somewhat from the ‚common form‘, and which thus was described as a distinct subspecies.
The Sakaraha Pygmy Kingfisher is now considered extinct, because no additional specimen could ever be located.
 Pete Morris, Frank Hawkins: Birds of Madagascar, A Photographic Guide. Yale University Press 1998  C. Hilary Fry, Kathie Fry, Alan Harris: Kingfishers Bee-eaters & Rollers. A & C Black 1999