The Australian Fritillary Butterfly (Argynnis hyperbius inconstans)
This is regarded as Australia's most endangered butterfly, which has not been sighted for decades. There is a fascinating article about the history of the Australian Fritillary butterfly available for free download - click here.
The article explains how there was a large colony of Australian Fritillary butterflies located in a gully of a horse paddock near Gympie, QLD. There were a lot of native violets (the butterfly's host plant) growing there, but unfortunately gully was bulldozed and levelled sometime after 1977, which destroyed the colony. There were three other smaller colonies identified in swamps near Caboolture, but these sites were also disturbed and over-run with invasive weeds, leading to habitat loss and the butterflies dispersal.
Even in 19th century, the Australian Fritillary was regarded as extremely rare, which made it desirable for butterfly specimen collectors, who were willing to pay high premiums for it. Around 1920, a dodgy taxidermist, Thomas Batcheler, sold two male specimens to the QLD Department of Agriculture and Stock Insect Collection, most likely for a premium price. Later it was realized that these were actually the Indian Fritillary (Argynnis hyperbius) butterfly. The males of both species are very similar, but the females are different. This deception was recently practiced again, with another male "Australian Fritillary" having supposedly been captured in QLD, but turned out to be another Indian Fritillary, actually purchased from a dealer in Thailand. You can read the full story, written by Trevor Lambkin from the University of QLD, in the article linked above.
The picture above is of the first drawing of an Australian Fritillary Butterfly, Argynnis hyperbius inconstans. It comes from a small book called "Australian Butterflies: a brief account of the native families", published in 1889. The illustration is of a male specimen.