CHOEISTODERA. 109 



Champsosaurus saponensis Cope. 



Paleontological Bulletin No. 34, p. 196 ; Feb. 20, 1882. Proceedings Amer. Philos. Society, Dec. 1881, 



p. 196, 1882. 

 Plate XXIII b ; figs. 11-22. 



Represented in my collection by six cervical and several dorsal verte- 

 brae; one only of the latter with well preserved centrum, parts of ribs, and 

 various other bones, whose reference is not yet certain. 



The cervical vertebrae include the os dentatum or centrum of the atlas. 

 This shows its streptotylicate character in its distinctness from both the cen- 

 trum and the free hypapophysis of the axis. Nevertheless, it is more Croc- 

 odilian than Lacertilian in form. Its anterior face is transverse, with a little 

 lip carrying forwards the floor of the neural canal, below which the face 

 is bevelled posteriorly. The inferior surface is narrow and transverse, as 

 though adapted for the anterior part of the hypapophysis of the axis. At 

 each side it terminates in a prominent tuberosity, as though for the attach- 

 ment of a cervical rib as in the Crocodilia. The anterior face is bounded 

 posteriorly by a transverse groove which terminates in a down-looking fossa 

 on each side. The i)osterior articular face of the os dentatum is wider than 

 deep. The lateral angles of the superior face are rounded, and its median 

 portion is concave. 



The axis displays a large facet for the hypapophysis. Behind it the infe- 

 rior middle line is not keeled, but is coarsely wrinkled longitudinally. The 

 posterior edge of the hypapophysial facet is the most prominent part of the 

 inferior surface. The posterior articular face is deeper than wide. This is 

 true of the faces of all the cervical vertebras. The latter gradually increase 

 in size posteriorly, and the dorsals become larger. The articular faces of 

 all the centra are regularly rounded and not contracted below. The five 

 cervicals are strongly keeled below, the keel of the third centrum being 

 split up anteriorly into narrow ridges On the sixth the keel is more prom- 

 inent and acute. The dorsal is not keeled. A trace of the parapophysis 

 appears low down on the fourth cervical ; it rises and becomes prominent 

 as a rounded tuberosity on the fifth and sixth. It appears on the superior 

 edge of the centrum of the dorsal vertebra, where it is connected with the 

 diapophysis. It is near the middle of the length of the centrum, and not 

 near the anterior border, as in C. australis. 



