Gr. λεπτος leptos  slender; ονυξ onux, ονυχος onukhos  claw. 
● (syn. Coryphaspiza Ϯ Black-masked Finch C. melanotis)  "LEPTONYX, Sw.  Bill intermediate between Emberiza and Ammodramus  ...  Feet as in Ammodramus; but the hind claw as long as its toe.   L. melanotis. Part 5. No. 100" (Swainson 1837). 
● (syn. Pteroptochos Ϯ Moustached Turca P. megapodius) "LEPTONYX macropus  Great-footed Babbler  ...  Feet of extraordinary size and thickness, all the anterior toes of nearly equal length; the claws long, slender, and but slightly curved.  ...  All the rasorial characters are strikingly displayed in this extraordinary type; which exhibits the greatest developement of the foot of any insessorial bird yet discovered. It no doubt lives entirely upon the ground; for the feet are formed precisely on the same model as those of Menura and Orthonyx" (Swainson 1832).   Var. Leptonix.

Search for more names on the Key to Scientific Names in Ornithology by James A. Jobling.
Recommended citation
Jobling, J. A. (2018). Key to Scientific Names in Ornithology. In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.) (2018). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from www.hbw.com on 15 December 2018).