She Cabbage Leaf Beetle (Longitarsus janulus)
The She Cabbage Leaf Beetle was described in 1877, it was endemic to the island of saint Helena in the middle of the Atlantic Ocean.
The species was apparently adapted to the likewise endemic She Cabbage tree (Lachanodes arborea (Roxb.) B. Nord.), a tree species that once was quite common on the High Central Ridge of the island, but which has virtually disappeared as a wild species now.
“The only spot in which I observed this very distinct Longitarsus is a little ravine below Halley’s Mount and between Oakbank and Hutt’s Gate, known as Vine-Tree Gut, – where it was extremely abundant on the foliage of the curious Lachanodes prenanthiflora [Lachanodes arborea], or “she cabbage-tree.” It is a rather larger insect than the L. helenae, and of not quite so lively a metallic green. Indeed its female sex is comparatively dull and opake, and has the elytra so wonderfully and deeply malleated down either outer disk as to cause the whole surface to appear coarsely wrinkled and (as it were) imperfectly developed, – leaving, however, three or four abbreviated longitudinal ridges (not so short as in the L. helenae) conspicuous within the excavation. Its males moreover differ from those of the L. helenae in having their antennae very much thicker or more developed, and in the basal joint of their four anterior feet being still more broadly expanded. Its prothorax too, in both sexes, is much more coarsely punctured than that of the L. helenae.” 
The She Cabbage Leaf Beetle was not found during the most recent field searches and is now almost certainly extinct. 
 T. Vernon Wollaston: Coleoptera Sanctae-Helenae. London: John Van Voorst, Paternoster Row 1877
 Howard Mendel; Philip Ashmole; Myrtle Ashmole: Invertebrates of the Central Peaks and Peak Dale, St. Helena. Report for the St Helena National Trust, Jamestown 2008