Ichthyosaurus^^ SI 



Place in the Geological Series. — Atlantic tertiary. The piece 

 of " sea-marr which accompanied the specimen is a conglomer- 

 ate mass of small marine shells, principally of an extinct species 

 of Corbula, similar to those observed in the same formation in 

 Alabama. Most of these shells are comminuted ; a few, how- 

 ever, remain perfect. On the upper surface of the mass, there 

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

 pieces of crystallized 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 structvu-e of these frag- 

 ments, as well as of the portions of teeth remaining in the 

 sockets, bear a close analogy to those of the Ichthyosaurus, but 

 the extreme length and breadth of the intermaxillary bone, 

 which projects beyond the extremities of the superior maxil- 

 laries, will distinguish 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 inter- 

 maxillary bone contains four teeth, two on each side, also bro- 

 ken, thus displaying in all ten teeth, in a space of alveolar pro- 

 cesses, 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 minutiae we 

 must refer to the volume above quoted. 



Locality. — In the vicinity of the Yellow-stone and Missouri 

 rivers. Missouri territory. 



Place in the Geological series. — Secondary limestone of the 

 sub-cretaceous group. 



We are indebted to Major N. A. Ware for the specimens, 

 who obtained them at St Louis, from a fur-trader or trap- 

 per, who, " on his return home from the Rocky Mountains, 

 observed in a rock the skeleton of an alligator animal, about 

 seventy feet in length ; he broke oft' the point of the jaw as it 



