THE CRETACEOUS PERIOD. 28 1 



the existing forms of the group in the fact that the bodies 

 of the vertebrae, like those of the Jurassic Crocodiles, are 

 bi-concave, or hollowed out at both ends. In the Greensand 

 of North America, however, occur the remains of Crocodiles 

 which agree with all the living species in having the bodies of 

 the vertebrae in the region of the back hollowed out in front 

 and convex behind. 



Birds have not hitherto been shown, with certainty, to have 

 existed in Europe during the Cretaceous period, except in a 

 few instances in which fragmentary remains belonging to this 

 class have been discovered. The Cretaceous deposits of 

 North America have, however, been shown by Professor 

 Marsh to contain a considerable number of the remains of 

 Birds, often in a state ..of excellent preservation. Some of 

 these belong to Swimming or Wading Birds, differing in no 

 point of special interest from modern birds of similar habits. 

 Others, however, exhibit such extraordinary peculiarities that 

 they merit more than a passing notice. One of the forms in 

 question constitutes the genus IcJitJiyornis of Marsh, the type- 

 species of which (/. dispar} was about as large as a Pigeon. 

 In two remarkable respects, this singular Bird differs from all 

 known living members of the class. One of these respects 

 concerns the jaws, both of which exhibit the Reptilian char- 

 acter of being armed with numerous small pointed teeth (fig. 

 212, a), sunk in distinct sockets. No existing bird possesses 

 teeth ; and this character forcibly recalls the Bird-like Ptero- 

 saurs, with their toothed jaws. Ichthyornis, however, possessed 

 fore-limbs constructed strictly on the type of the "wing" of the 

 living Birds; and it cannot, therefore, be separated from this 

 class. Another extraordinary peculiarity of Ichthyornis is, that 

 the bodies of the vertebra (fig. 212, c) were bi-concave, as is the 

 case with many extinct Reptiles and almost all Fishes, but as 

 does not occur in any living Bird. There can be little doubt 

 that Ichthyornis was aquatic in its habits, and that it lived prin- 

 cipally upon fishes ; but its powerful wings at the same time 

 indicate that it was capable of prolonged flight. The tail of 

 Ichthyornis has, unfortunately, not been discovered ; and it is 

 at present impossible to say whether this resembled the tail of 

 existing Birds, or whether it was elongated and composed of 

 'separate vertebrae, as in the Jurassic Archaopteryx. 



Still more wonderful than Ichthyornis is the marvellous bird 

 described by Marsh under the name of Hesperornis regalis. 

 This presents us with a gigantic diving bird, somewhat re- 

 sembling the existing "Loons" (Colymbus), but agreeing 

 with Ichthvornis in having the jaws furnished with conical, 



