282 



HISTORICAL PAL/EONTOLOGY. 



recurved, pointed teeth (fig. 212, b}. 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; 



Fig. 212. Toothed Birds (Otlontortiittus) 

 Left lower jaw of Ichthyornis dispar, slightly enlarged ; b, Left lower jaw of Hesperornis 



of the Cretaceous Rocks of America, a, 



ower aw of Ichthyornis dispar, slightly enlarged ; b, Left lower jaw of Hesperor 

 ecall's, reduced to nearly one-fourth of the natural size ; c, Cervical vertebra oS Ickthyo 

 dispar, front view, twice the natural size ; </, Side view of the same ; d, Tooth of Hesper- 

 ornis regalis, enlarged to twice the natural size. (After Marsh.) 



but instead of being sunk in distinct 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 Hcsperornis, 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 vertebras, of which the last three or 

 four are amalgamated to form a flat terminal mass, there being 

 at the same time clear indications that the tail was capable 

 of up and down movement in a vertical plane, this proba- 

 bly fitting it to serve as a swimming-paddle or rudder. The 

 legs were powerfully constructed, and the feet were adapted to 

 assist the bird in rapid motion through the water. The known 

 remains of Hesperornis regalis prove it to have been a swim- 

 ming and diving bird, of larger dimensions than any of the 



