A new species of the genus Cyathodium Kunze, C. mehranum Singh, has been described from Bomdila (Kameng), Arunachal Pradesh, India. The species is characterised by the thallus showing a tendency towards having more than single layered air chambers; lacking of an established nature of the dorsal pores; presence of tubers usually on both male as well as female plants; pubescent involucres with thick-walled and deeply pigmented marginal cells; presence of apically fixed elaters; annular thickening bands in the cells of the capsule wall with nodulose radial wall thickenings, besides the presence of spiral thickenings on the inner tangential walls and double sculptured spores with muricate ornamentations interspersed with laevigate, 3-7 μm high baculae.