HI LECTURES ON EVOLUTION 95 



tion. By his kindness, I am enabled to place 

 before you a restoration of one of these extraor- 

 dinary birds, every part of which can be thoroughly 

 justified by the more or less complete skeletons, in 

 a very perfect state of preservation, which he has 

 discovered. This Hesperornis (Fig. 3), which 

 measured between five and six feet in length, is 

 astonishingly like our existing divers or grebes in a 

 great many respects ; so like them indeed that, 

 had the skeleton of Hesperornis been found in a 

 museum without its skull, it probably would have 

 been placed in the same group of birds as the 

 divers and grebes of the present day. 1 But 

 Hesperornis differs from all existing bir.! ., and so 

 far resembles reptiles, in one important particular 

 it is provided with teeth. The long jaws are 

 armed with teeth which have curved crowns and 

 thick roots (Fig. 4), and are not set in distinct 

 sockets, but are lodged in a groove. In possessing 

 true teeth, the Hesperornis differs from every ex- 

 isting bird, and from every bird yet discovered in 

 the tertiary formations, the tooth-like serrations of 

 the jaws in the Odontopteryx of the London clay 

 being mere processes of the bony substance of the 

 jaws, and not teeth in the proper sense of the word. 

 In view of the characteristics of this bird we are 



1 The absence of any keel on the breast-bone and some other 

 osteotogical peculiarities, observed by Professor Marsh, however, 

 suggest that Hesperornis may be a modification of a less 

 specialised group of birds than that to which these existing 

 aquatic birds belong. 



