The Norfolk Island Pigeon is still often regarded to as a subspecies of the New Zealand Pigeon (Hemiphaga novaeseelandiae (Gmelin)) but clearly constitutes a distinct species.
The species reached a size of 50 cm and differed from the New Zealand Pigeon mainly by the coloration of its wings, which were grey instead of green.
The Norfolk Island Pigeon was apparently last recorded in 1838 and appears to have been gone just by one year later, the reasons for its extinction are overhunting but also predation by introduced mammals, especially cats.
Napean Island Amber Snail (Spirancinea napeanensis)
This species was described in 1913 based on subfossil shells that were found on the tiny Napean Island offshore the southern coast of Norfolk Island. The shells show a wide variability and thus were originally described as two species, which subsequently were synonymized with each other.
The Napean Island form could well be conspecific with the Norfolk Island Amber Snail (Spirancinea norfolkensis (Sykes)) or could be assigned to that species as a subspecies.
 Tom Iredale: The Land Mollusca of Norfolk Island. The Australian Zoologist 11: 46-71. 1945-1951