520 THE OLDEST KNOWN MAMMALIA. 



the intervertebral articulation, which varies in the caudal region of 

 existing birds, remain embryonic. We should explain in the same 

 way the ligamentous union of the jaws ; and regard the presence of 

 teeth as an embryonic character lost in living birds, much as teeth are 

 lost in the adult whalebone whales. Hence we refer Ichthyornis 

 to the natatorial group of birds. Professor Marsh has described 

 many other cretaceous birds under the names Apatornis, Baptornis, 

 Graculavus, Laornis, Palceotringa, and Telmatornis. 1 



The fossil birds of the Tertiary rocks of Europe have been described 

 in detail by Professor Alphonse Milne-Edwards, 2 but the most remark- 

 able of these remains occur in the Lower Tertiary beds of the Paris 

 basin, from which they have been described by Professor Victor 

 Lemoine, who figures Gastoniis, uptromit t and lienicornis. Gas- 

 tornis was a struthious bird, which may have stood 7 or 8 feet high. 



Struthious birds found in our own Tertiary strata are represented 

 in the London Clay by Dasornis, imperfectly known from the skull, 

 which is considered to resemble the Dinornis of New Zealand. Frag- 

 mentary remains indicate the kingfisher Halcyornis, the vulture 

 Lithornis, besides birds like the heron and sea-swallows. The 

 albatross is represented by an allied genus, Argillorni*, and Odontap- 

 teryx is a bird with some affinities to the duck tribe, which had long 

 bony teeth on the jaw, which was probably covered with horn. A 

 struthious bird referred to the genus Macornis is found in the Headon 

 beds of the Isle of Wight, and some other birds are known from the 

 Hempstead beds and the Eracklesham beds. 



Evolution and Succession of Mammalia. The oldest mammals 

 are chiefly known from teeth. Molar teeth of Microlestes, from the 

 Rhsetic beds in this country, and Keuper beds of the Trias of Germany, 

 are shown by the premolar teeth, named Hypsiprymnopsis, to so closely 

 resemble Plagiaulax of the Purbeck beds, and the living kangaroo-rat 

 Hypsiprymnus, that we may affirm descent without recognised modi- 

 fication of plan. Under the name Neoplagiaulax, Dr. Lemoine has de- 

 scribed a near ally of Plagiaulax from the Lower Tertiary rocks. One of 

 the most interesting of recent discoveries is the skull of the South Afri- 

 can Triassic mammal, named by Sir Richard Owen 2'ritylodon, which 

 has three longitudinal rows of cusps on the molars, closely resembling 

 the Triglyphus of Fraas from the Trias of Stuttgart. Professor Cope 

 has found a representative of the type in the Tertiary beds of North 

 America, which is named Polymastodon. 3 The lower jaws of mam- 

 mals from the Stonesfield slate, termed Amphitherium and Pkascolo- 

 therium, with strong marsupial characters, combine many characters 

 of the Insectivora, and are associated with a humerus and femur which 

 indicate a generalised Insectivorous type, modified from a Monotreme 

 stock in the direction of the marsupial plan. 4 The only mammal from 



1 Odontornithes : Extinct toothed birds of North America, by O. C. Marsh. 



2 " Recherches anatomiques et paldontologiques 1'histoire des oiseaux fossiles 

 de la France." 4to. 1867-74. 



;i Cope : "The Tertiary Marsupial ia, " American Naturalist, July 1884. 

 4 Q. J. G. S., August 1879. 



