112 ODONTORNITHES. 



In the preceding Plates, I-XIX, the bones of Hesperornis regalis have 

 "been represented in natural size, and the magnitude of the whole bird may 

 be judged from the fact that the skeletou, if extended, would measure 

 about six feet (1.8 M ) from the point of the bill to the end of the toes. 

 Hesperornis crassipes was somewhat larger, and Hesperornis gracilis, so far 

 as known, was apparently smaller, and of more delicate proportions. 

 When on land in the position represented in Plate XX, Hesperornis regalis 

 would be rather more than three feet in height. 



Hesperornis was a typical aquatic bird, and in habit was doubtless 

 very similar to the Loon, although, flight being impossible, its life was 

 probably passed entirely upon the water, except when visiting the shore 

 for the purpose of breeding. The nearest land at that time was the suc- 

 cession of low islands which marked the position of the present Rocky 

 Mountains. In the shallow tropical sea, extending' from this land five 

 hundred miles or more to the eastward, and to unknown limits north and 

 south, there was the greatest abundance and variety of fishes, and these 

 doubtless constituted the main food of the present species. Hesperornis, as 

 Ave have seen, was an admirable diver, while the long neck with its 

 capabilities of rapid flexure, and the long slender jaws armed with sharp 

 recurved teeth formed together a perfect instrument for the capture and 

 retention of the most agile fish. As the lower jaws were united in front 

 only by cartilage, as in Serpents, and had on each side a joint which 

 admitted of some motion, the power of swallowing was doubtless equal to 

 almost any emergency. 



Having thus shown what the skeleton of Hesperornis is, and what its 

 mode of life must have been, it remains to consider the more important 

 question of how the peculiar combination of general and specialized 

 characters manifested in its structure originated. The two most striking 

 features of Hesperornis are the teeth, and the limbs, and an inquiry in 

 regard to them first suggests itself. 



The teeth of Hesperornis may be regarded as a character inherited 

 from a reptilian ancestry. Their strong resemblance to the teeth of 



