Nyctibatrachus

Nyctibatrachus is a genus of frogs endemic to the Western Ghats of southwestern India. Their common name is night frogs. Their scientific name also means "night frog". 
These frogs are quite common, and researchers think this has been overlooked because of their their small size. They are indeed extremely small, and can sit on a coin or a fingernail. However, they are not so small as "Paedophryne", which is the smallest land vertebrate.