The genus Acanthoptila was instituted by Blyth for a remarkable bird discovered by Hodgson many years previously, and which is still very rare. It is characterized by its large size, spinous plumage, and very ample tail.
Hodgson figures two specimens, to each of which he assigns a different name; but an examination of his types, together with some other specimens, leaves it little doubtful, I think, that both drawings represent the same species, and that the differences shown are due to season. Acanthoptila, like most Warblers, has two moults a year, probably only a partial one in the spring, but one which affects the colour of the throat very distinctly. The sexes are probably alike.
This genus has a bill nearly as long as the head and gently curved; the rictal bristles are short, there are no supplementary hairs, and the forehead is flat and smooth as in other Grass-Warblers. The wing is rounded, and the first four quills graduated. The tail is much longer than the wing, broad and well rounded. The tarsus is about one third the Length of the wing and very strong.