ICHTHYOEXITHES 47] 



ences in detail. In Apatornis there is a very long acromial 

 process. The coracoids overlap at their articulation with the 

 sternum, more so in Ichthyornis than in Apatornis. The 

 clavicles are generally figured as typically carinate ; but the 

 only part of this bone known is ' a fragment from the upper 

 end of that bone in Apatornis.' The sternum is deeply 

 keeled. 



The bones of the fore limb are well developed; the 

 humerus has a very large crest, surpassing in comparative 

 size that of any recent bird ; this clearly indicates a powerful 

 flyer, and the rest of the bones of the Hmb bear out this view. 

 Though nothing is known of the structure of the feathers, 

 there are upon the ulna impressions for the quill feathers. 



In the pelvis all the bones are free posteriorly, as in Hes- 

 perornis, Apteryx, &c. The acetabulum is perforate, as in 

 most recent birds ; but the perforation is of moderate size, as 

 in the tinamous. 



In the neighbourhood of Ichthyornis are possibly to be 

 placed Marsh's genera Baptornis, Telmatornis, and Sbeley's 

 Enaliornis. These birds, however, Cretaceous, like Hesper- 

 ornis and Ichthyornis, are known by such limited material 

 that their position is absolutely uncertain. 



The affinities of Ichthyornis to Hesperornis have been 

 dwelt upon by some ; but it appears that Ltdekkbe's 

 remark, that ' the Odontornithes are a series of birds ances- 

 tral to the modern series of toothless carinates,' expresses the 

 truth. He has furthermore added that this series ' differs 

 from the Euornithes (Stejneger's name for carinates) by the 

 absence of union between the rami of the mandible and 

 between the distal ends of the ischium and ilium,' likenesses 

 which do not mean a near rela/tionship, but express the 

 degree of development of bird structure at that period. 



