2QO HISTORICAL PALEONTOLOGY. 



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 Ichthyornis of Marsh, the type 

 species of which (7. disbar} 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. 213, 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 Iththyornis 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 Arcliceopteryx. 



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 Ichthyornis in having the jaws furnished with conical, 

 recurved, pointed teeth (fig. 212, fr). Hence these forms are 

 grouped together in a new sub-class, under the name of Odon- 

 'tornithes or "Toothed Birds." The teeth of Hesperornis (fig. 

 212, d~) resemble those of Ichthyornis in their general form; 

 but instead of being sunk in distant sockets, they are simply 

 implanted in a deep continuous groove in the bony substance 

 of the jaw. The front of the upper jaw does not carry teeth, 

 and was probably encased in a horny beak. The breast-bone 

 is entirely destitute of a central ridge or keel, and the wings 

 are minute and quite rudimentary; so that Hesperornis, unlike 

 Ichthyornis, must have been wholly deprived of the power of 

 flight, in this respect approaching the existing Penguins. The 

 tail consists of about twelve vertebrae, of which the last three or 



