RESTORATION OF ICHTHTORNIS. 183 



(1.) Biconcave vertebra (Fishes and Amphibians) ; the primitive type ; 

 a weak articulation, admitting free, but limited motion. From this form, 

 have been directly derived the other varieties, namely : 



(2.) Plane vertebrce (Mammals) ; affording a stronger joint, with motion 

 still restricted. 



(3.) Cup-and-ball vertebrce (Reptiles) ; a strong and flexible joint, well 

 fitted for general motion, and evidently produced by it. The vertebrae are 

 procoelian when lateral motion is dominant (Serpents) ; opisthocoelian with 

 varied motion (Dinosaur cervicals). 



(4.) Saddle vertebrce (Birds) ; the highest type ; a very strong and free 

 articulation, especially adapted to motion in a vertical plane, and mainly 

 due originally to its predominance. 



In considering the mode of life, and habits of Ichtliyomis, many 

 important suggestions may be derived from its structure, as well as from 

 the localities where the remains are found. The sharp cutting teeth 

 of Ichtliyomis prove, beyond a doubt, that it was carnivorous ; its great 

 powers of flight, long jaws, and its recurved teeth suggest, moreover, that 

 it captured its prey alive. Its food was probably fishes, as their remains 

 are found in great abundance mingled with those of Ichtliyomis. These 

 fossils occur in the bed of the old Cretaceous ocean in which Hesperornis 

 swam. Both of these birds were clearly aquatic in habit, as shown by 

 various points in their structure, already described, and the conditions 

 under which their remains were deposited. In many respects, Ichtliyomis 

 probably resembled the modem Terns in its mode of life. The powerful 

 wings and small feet suggest similar habits in flight, and rest. That 

 Ichtliyomis was provided with feathers is proved beyond question by the 

 tubercles for the attachment of quills on the forearm. 



Beside Ichtliyomis and its allies, the only other denizens of the ah- at 

 present known to have then inhabited the same region were the toothless 

 Pterodactyles. Ichtliyomis doubtless competed with these huge dragons 

 for the fishes in the tropical ocean, about which they lived. 



