In the Eocene we find ourselves almost wholly among extinct forms of birds. The earliest known Passerine bird is here met with, in _Protornis_, somewhat similar to a lark, found in the Lower Eocene of Switzerland; while another Passerine form, _Palægithalus_, and one allied to the nuthatch (_Sitta_), have been {163}discovered in the Upper Eocene of Paris. Picariæ of equal antiquity are found. _Cryptornis_, from the Paris Eocene, and _Halcyornis_ from the Lower Eocene of the Isle of Sheppey, were both allied to kingfishers; while a form allied to _Centropus_ a genus of cuckoos, or, as Milne-Edwards thinks, to the Madagascar _Leptosomus_, has been found in the Upper Eocene of France. Several _Accipitres_ of somewhat doubtful affinities have been found in the same country; while _Lithornis_, from the Lower Eocene of the Isle of Sheppey, was a small vulturine bird supposed to be allied to the American group, _Cathartes_. Among the waders, some extinct forms of plovers have been found, and a genus (_Agnopterus_), allied to the flamingoes; while there are many swimming birds, such as pelicans, divers, and several extinct types of doubtful affinities. Most intersting of all is a portion of a cranium discovered in the Lower Eocene of Sheppey, and lately pronounced by Professor Owen to belong to a large Struthious bird, allied to the New Zealand _Dinornis_ and also perhaps to the ostrich. Another gigantic bird is the _Gastornis_, from the Lower Eocene of Paris, which was as large as an ostrich, but which is believed to have been a generalised type, allied to wading and swimming birds as well as to the Struthiones. Beyond this epoch we have no remains of birds in European strata till we come to the wonderful _Archæopteryx_ from the Upper Oolite of Bavaria; a bird of a totally new type, with a bony tail, longer than the body, each vertebra of which carried a pair of diverging feathers. _North America._--A number of bird-remains have lately been found in the rich Tertiary and Cretaceous deposits of the United States; but here, too, comparatively few are terrestrial forms. No Passerine bird has yet been found. The Picariæ are represented by _Uintornis_, an extinct form allied to woodpeckers, from the Eocene of Wyoming. Species of turkey (_Meleagris_) occur in the Post-Pliocene and as far back as the Miocene strata, showing that this interesting type is a true denizen of temperate North America. The other birds are, _Accipitres_; waders and aquatics of existing genera; and a number of extinct forms of the two latter orders--such as, _Aletornis_ an Eocene wader; {164}_Palæotringa_, allied to the sandpipers, and _Telmatobius_ to the rails, both Cretaceous; with _Graculavus_, allied to _Graculus_; _Laornis_ allied to the swans; _Hesperornis_ a gigantic diver; and _Icthyornis_ a very low form, with biconcave vertebra, such as are only found in fishes and some reptiles--also from Cretaceous deposits.