124 ODOXTORXITHES. 



The dentigerous portion of the lower jaw is so similar to that of 

 some of the smaller Mosasauroid Keptiles, that, without other portions of 

 the skeleton, the two could hardly be distinguished. 



The Teeth. (Plate XXL) 



The teeth of IcMJiyomis were implanted in distinct sockets, thus 

 differing- widely from those of Hesperornis. They are all sharp and pointed, 

 more or less compressed, and strongly recurved. The crowns are coated 

 with enamel, and the two fore and aft cutting edges are sharp and 

 smooth, without serrations. 



The maxillary teeth appear to have been larger than those opposing 

 them. Their alveolar cavities are crowded together, and yet distinctly 

 separated from each other by a thin septum of bone. They are oval in 

 outline, and quite shallow, owing to the small vertical extent of the 

 maxillary (Plate XXI, figure 1, and la). Whether the premaxillary 

 bones contained teeth is uncertain, but they were probably edentulous, 

 as in Sesperornis. 



The dental cavities in the lower jaw are elliptical in outline, and vary 

 in size according to position. They are in general deeper, and separated 

 more widely from each other, than those in the maxillaries. In the right 

 lower jaw of the type specimen of Ichthyornis clispar, there are twenty- 

 one distinct sockets. The anterior one is very near the extremity, and 

 contains a tooth of moderate size. The largest teeth in the lower jaw 

 are just back of the middle of the dentary bone. From this region to 

 the posterior end of the dentary, the teeth diminished gradually in size. 

 The whole surface of each tooth exposed above the jaw is covered with 

 smooth enamel. In the right lower jaw of the type specimen, there 

 are eight teeth still in their sockets, and from these the others have been 

 restored in outline, as shown in Plate XXI. 



In IcMlujomis anceps (number 1749), the lower jaws are more slender 

 than in the type species, and the number of teeth greater. The anterior 

 half of the dentary contained large teeth only. The posterior eleven teeth 

 were all small, and nearly uniform in size. 



