CATALOGUE 



01' TiJK 



C II E L O N I A N S. 



lillYNCUOCEniALIANS, 



AND 



EMYDOSAIJRIANS. 



Order RHYNCHOCEPHALIA. 



Ivhyuclioceplialia, Giinther, Phil. Trans, clvii. 18G7. 



Quadrate bone immovably united to cranial arches ; two hori- 

 zontal bony temporal arches. Dorsal ri])s single-headed, articulating 

 with the centrum and the neural arch. A well-developed sternal 

 apparatus and a plastron, the latter formed of very numerous splint- 

 like bones or " abdominal ribs," each composed of three pieces 

 forming an obtuse angle directed forwards, and situated in tlie sub- 

 cutaneous ligamentous tissue*. Teeth present, not implanted in 

 alveoli. Anal cleit transverse. Copulatory organs none. 



The " Lizards " constituting this Order may be regarded as the 

 most generalized of all recent and, perhaps, of all known Pieptilia : 

 in many points they approach the Stegocephalian Hatrachians ; 

 it is possible that the common ancestors of the Chelonia, the 

 Plesiosauria, and the Lacertilia would fall in this Order. The 

 affinities of the lUiynchocephalia to the Chelonia arc at least as 

 great as to the Lacertilia. Only one species has survived to the 

 present day, the Sphenodon of New Zealand, which is closely allied 

 to, though less specialized than, the forms of the Trias : its claims 

 to being the oldest existing Keptilian type are therefore unques- 

 tionable. 



* It is noteworthy, as the fact does not appear to huTe been poiDted out 

 before, tliat the anterior extremity of the plastron overlaps the posterior 

 extremity of the sternum. 



B 



