The genera of birds peculiar to this sub-region belong to the following families:--Turdidæ (2 genera); Troglodytidæ (1 gen.); Vireonidæ (1 gen.); Corvidæ (2 gen.); Ampelidæ (1 gen.); Tanagridæ (1 gen.); Fringillidæ (2 gen.); Icteridæ (1 gen.); Formicariidæ (2 gen.); Tyrannidæ (2 gen.); Cotingidæ (1 gen.); Momotidæ (1 gen.); Trogonidæ (1 gen.); Trochilidæ (14 gen.); Conuridæ (1 gen.); Cracidæ (2 gen.); Strigidæ (1 gen.); in all 37 genera of land-birds. The Neotropical families that do not extend into this sub-region are, Pteroptochidæ; the sub-family _Furnariinæ_ of the Dendrocolaptidæ; the sub-family _Conophaginæ_ of the Tyrannidæ; the sub-family _Rupicolinæ_ of the Cotingidæ; Phytotomidæ; Todidæ; Opisthocomidæ; Chionididæ; Thinocoridæ; Cariamidæ; Psophiidæ; Eurypygidæ; Palamedeidæ; and Struthionidæ. On the other hand Paridæ, Certhiidæ, Ampelidæ, and Phasianidæ, are northern families represented here, but which do not reach South America; and there are also several northern genera and species, of Turdidæ, Troglodytidæ, Mniotiltidæ, Vireonidæ, Fringillidæ, Corvidæ, Tetraonidæ, and Strigidæ, which are similarly restricted. Some of the most remarkable of the Neotropical genera only extend as far as Costa Rica and Veragua,--countries which possess a rich and remarkable fauna. Here only are found an umbrella bird, (_Cephalopterus glabricollis_); a bell bird (_Chasmorhynchus tricarunculatus_); and species of _Dacnis_ (Ceroebidæ), _Buthraupis_, _Eucometis_, _Tachyphonus_ (Tanagridæ), _Xiphorhynchus_ (Dendrocolaptidæ); _Hypocnemis_ (Formicariidæ); _Euscarthmus_ (Tyrannidæ); _Attila_ (Cotingidæ); _Piprites_ (Pipridæ); _Capito_, _Tetragonops_ (Megalæmidæ); _Selenidera_ (Rhamphastidæ); _Neomorphus_ {54}(Cuculidæ); _Monasa_ (Bucconidæ); many genera of Trochilidæ; and _Nothocercus_ (Tinamidæ); none of which extend further north. A considerable number of the peculiar genera noted above, are also found in this restricted area, which is probably one of the richest ornithological districts on the globe.