BIRDS FROM CRETACEOUS ROCKS. 519 



the bird plan, with teeth in the premaxillary and maxillary bones. 

 The teeth were in distinct sockets, and appear to have resembled in 

 plan the teeth of Mosasaurus. The tail is elongated as in some 

 ornithosaurs, and the character from being previously unknown 

 among birds has an ordinal value: it suggests the name Saururiae. 

 The digits of the fore limb are distinct from each other ; they are 

 three in number, and each terminates in a claw. These characters 

 are differences from existing birds, but although often taken to 

 indicate a resemblance to ornithosaurs, there is nothing reptilian in 

 the skeleton of the Archseopteryx, except that it is less specialised 

 than the skeleton in existing groups of birds. Feathers in all respects 

 similar to the feathers of existing birds were developed. We are 

 indebted to Professor Dames for the figure of the head. The only 

 specimens known are in the Royal Museum at Berlin, and the British 

 Museum ; they are from the Solenhofen Slate. 



An American Jurassic bird has been described by Marsh under the 

 name Laopteryx. It is rather larger than a blue heron, but only an 

 imperfectly-preserved skull is described. 



Cretacaous birds were first discovered in the Upper Greensand of 

 Cambridge. They are known from fragments, which however proved 

 that some of the vertebrae are bi-concave in the back, that the avian 

 form of articulation exists in the neck, that the head resembles the 

 divers, that the tibia is like that of the grebes, while the pelvis has 

 some characters in common with the penguins. These birds have been 

 referred to the genus Enaliornis ; but a larger bird existed with them, 

 in which the extremities of the long bones were not ossified. In 

 America Professor Marsh has described, under the name Odontor- 

 nithes, two genera of toothed birds. One of large size named Hesper- 

 omis had a very reptilian type of brain. Its teeth are like the teeth 

 of Arcliceopteryx ; the sternum has no keel ; its scapular arch is 

 small, and the fore limb is represented by a rudimentary humerus. 

 The pelvic arch is not struthious ; it is only anchylosed to the sacrum 

 in the acetabular region. The acetabulum is closed by bone. The 

 nearest approach to the legs and feet of Hesperornis is seen in the 

 genus Podiceps. The bird is regarded as having been aquatic, inca- 

 pable of flight, with habits comparable to those of the loon. The 

 animal is classed as a carnivorous swimming ostrich. We should 

 rather say a carnivorous natatorial bird, which had not evolved or lost 

 carinate characters. The resemblances of classificational value are all 

 with the water-birds. The resemblances to the ostrich show the 

 direction of the parent stock from which water-birds became evolved. 



Ichthyornis is so named because the articular ends of the vertebrae are 

 bi-concave as in fishes. The bird had the wings well developed. Professor 

 Marsh remarks that it can be interpreted by supposing that certain parts 

 have become highly specialised in the direction of the evolution of re- 

 cent birds, while others have been derived with but little change from 

 reptilian, or even a more lowly ancestry. We should have preferred 

 to say that all the structures which functional conditions have made 

 distinctive of birds are well marked, while some other characters, like 



