CIIELONIA. 5 



Fam. 4. Cinosternidae. Caudal vertrbno procalous; plastral bones 

 c'iii;lit, the c'liloijlastruu being- absent; pubic and iscliiul 

 S5'mph3scs in contact, separating two foramens. 



B. Nuchal phito without costiform processes ; symphysial branches 

 of pubis and ischium paralkl, in contact or narrowly sepa- 

 rated from each other. 



Fam. 5. Platysternidae. Caudal vertebnc mostly opislhocffilous. 



Fam. 6. Testudinidse. Caudal vertebia; proccelous. 



II. Limbs paddle-sluiped ; ])halanj?es without condj'les ; claws one 

 or two. Keck inconi])letely retractile ; cervical vertebra) sliort, 

 mostly articidated by anijthiarthrosis. Squamosal bono tbrining 

 a suturo with the parietal. 



Fam. 7. Chelonidae. 



Supcrfam. B. PLEURODIKA. 



Neck bending laterally; cervical vertebra; with strong transverse 

 processes, the cup-and-ball articulation single throughout; centrum 

 of the last cervical articulating with the centrum of the first dorsal. 

 !M audible with an artieulary condyle tilting into a concavity of the 

 quadrate ; outer border of tympanic cavity completely encircled by 

 the quadrate : pterygoids very broad throughout, forming wing-like 

 lateral expansions, and in contact on the median line. Pelvis 

 anchylosed to the carapace and plastron. Digits with not more 

 than three phalanges. Epi})lastra in contact with hyoplast ra ; 

 entoplastron oval or rhomboidal. A complete series of marginal 

 bones, connected with the ril)S. 



Fam. 8. PelomedusidaB. Plastral bones eleven, mcsoplastra being 

 present. Neck completely retractile within the shell. 



Fam. 9. ChelydidaB. Plastral bones nine. Neck bending under 

 the margin of the carapace, always exposed. 



Fam. 10. Carettochelydidse. Shell without epidermic shields. 

 Limbs paddle- shaped, with only two claws. 



Supcrfam. C. TRIONYCHOIDEA. 



Neck bending by a sigmoid curve in a vertical plane ; cervical 

 vertebrae without transverse processes ; articulation between the 

 last cervical and the first dorsal vertebra by the zygapophyses only. 

 Mandible with artieulary concavities ; outer border of tympanic 

 cavity notched ; pterygoids broad throughout, separated from each 

 other, the basisphenoid joining the palatines. Pelvis not anchylosed 

 to the carapace and plastron. Fourth digit with four or more pha- 

 langes. Epiplastra separated from the hyoplastral)y the /\ -shaped 

 entoplastron. Marginal bones absent or forming an incomplete 

 series, not connected with the ribs. 



Fam. 11. Trionychidse. 



