80 



TRANSACTIONS OF THE 



main perfect. On the upper surface of the mass, there 

 remains a stratum of clay half an inch in thickness, in- 

 closing pieces of chrystallized carbonate of lime. 



Genus Ichthyosaurus, Conybeare. 



I. Missouriensis, Harlan, ut supra, p. 405. 



The fossil fragments which indicate the existence of 

 the above named species, consist of the anterior portions 

 of the upper and lower jaws. The form and structure 

 of these fragments, as well as of the portions of teeth re- 

 maining in the sockets, bear a close analogy to those 

 of the Ichthyosaurus, but the extreme length and 

 breadth of the intermaxillary bone, which projects be- 

 yond the extremities of the superior maxillaries, will dis- 

 tinguish it from all other species of this genus hitherto 

 described. 



The portions of maxillary bones attached contain 

 three teeth on each side ? all equally broken off at the 

 sockets; the intermaxillary bone contains four teeth, 

 two on each side, also broken ; thus displaying in all 

 ten teeth, in a space of alveolar processes four inches 

 long, the length of the fragment. The mode of growth 

 and reproduction of the teeth is well displayed in the 

 fractured portions which remain ; the animal is allied 

 to the Ichthyosaurus in these particulars. For further 

 minutise we must refer to the volume above quoted. 



Locality. In the vicinity of the Yellow- stone and 

 Missouri rivers. Missouri territory. 



