CHORISTODERA. 105 



cepting a longitudinal carina, which ceases to exist on the dorsal vertebrae. 

 The zygapophyses are simple. The chevron bones are free. 



The relations of the atlas and axis, though not fully elucidated by my 

 specimens, are peculiar. The former has separate neurapophyses, which 

 have nearly the shape of those of the Streptostylicate Reptilia, resembling 

 much those of the Pythonomorpha. Although I procured numerous cervical 

 vertebrae, there are but few which exhibit the antero-inferior facet for sup- 

 posed hypapophysis, already described. The position of this vertebra was 

 in front of the first cervical which displays a parapophysis, and is, on this 

 account, likely to be the axis or the third cervical vertebra. It is the more 

 probably the axis, as there is no other among the large number of verte- 

 brae in my collection which can be referred to that position. Its anterior 

 articular face is smooth and like the posterior, showing that the odontoid 

 bone was not coossified with it. Now in the Crocodilia the odontoid bone 

 is united with the anterior extremity of the axis by suture, which may be- 

 come coossified with age, while the free hypapophysis is w^anting. In the 

 streptostylicate orders the hypapophysis is present, and the odontoid is above 

 it, but united to the axis by suture. On the other hand, in the Rhyncho- 

 cephalia, the axis is coossified with both odontoid and hypapophysis, and a 

 few succeeding vertebrae possess fre^ hypapophyses. 



A few entire ribs and the heads of many others have been obtained. 

 The cervical ribs are long, and the dorsals are relatively stout and shoi-t 

 The head of an anterior dorsal is truncate and compressed, its articular face 

 contracted, forming a narrow figure eight. The shaft is obliquely flattened. 

 The extremities are separated from the lateral surfaces by a narrow angle, 

 as though capped with cartilage in life, as in the Pythonomorpha. 



Bones of the extremities are very rare. One fragment resembles the 

 proximal end of a crocodilian tibia, and another is like the distal half or 

 more of the tibia of the same type. 



The above characters were derived from the Laramie species, and those 

 of the Puerco agree with them exactly in those respects. The latter enable 

 me to add, that the jaws are slender, and that the splenial bone of the man- 

 dible is well produced anteriorly. The teeth are set in shallow alveoli, and 

 are replaced from the inner side as in Lacertilia and Pythonomorpha. 



