CATALOGUE 
OF TBE 
CHELONTIANS, 
RHYNCHOCEPHALIANS, 
AND 
EMYDOSAURIANS. 
Order RHYNCHOCEPHALIA. 
Kthynchocephalia, Giinther, Phil. Trans. clvii. 1867. 
Quadrate bone immovably united to cranial arches; two hori- 
zontal bony temporal arches. Dorsal ribs 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 the sub- 
cutaneous ligamentous tissue*. Teeth present, not implanted in 
alveoli. Anal cleft transverse. Copulatory organs none. 
The “ Lizards” constituting this Order may be regarded as the 
most generalized of all recent and, perhaps, of all known Reptilia ; 
in many points they approach the Stegocephalian Batrachians ; 
it is possible that the common ancestors of the Chelonia, the 
Plesiosauria, and the Lacertilia would fall in this Order. The 
affinities of the Rhynchocephalia to the Chelonia are 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 Reptilian type are therefore unques- 
tionable. 
* Tt is noteworthy, as the fact does not appear to have been pointed out 
before, that the anterior extremity of the plastron overlaps the posterior 
extremity of the sternum. 
B 
