CHELONIA. 5 
Fam. 4. Cinosternide. Caudal vertebrz procclous ; plastral bones 
eight, the entoplastron being absent; pubic and ischial 
symphyses in contact, separating two foramens. 
B. Nuchal plate without costiform processes ; symphysial branches 
of pubis and ischium parallel, in contact or narrowly sepa- 
rated from each other. 
Fam. 5. Platysternidz. Caudal vertebre mostly opisthoccelous. 
Fam. 6. Testudinide. Caudal vertebre proccelous. 
II. Limbs paddle-shaped ; phalanges without condyles; claws one 
or two. Neck incompletely retractile; cervical vertebre short, 
mostly articulated by amphiarthrosis. Squamosal bone forming 
a suture with the parietal. 
Fam. 7. Chelonide. 
Superfam. B. PLEURODIRA. 
Neck bending laterally ; cervical vertebrxe with strong transverse 
processes, the cup-and-ball articulation single throughout; centrum 
of the last cervical articulating with the centrum of the first dorsal. 
Mandible with an articulary condyle fitting 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. Epiplastra in contact with hyoplastra; 
entoplastron oval or rhomboidal. A complete series of marginal 
bones, connected with the ribs. 
Fam. 8. Pelomeduside. Plastral bones eleven, mesoplastra being 
present. Neck completely retractile within the shell. 
Fam. 9. Chelydide. Plastral bones nine. Neck bending under 
the margin of the carapace, always exposed. 
Fam. 10. Carettochelydidz. Shell without epidermic shields. 
Limbs paddle-shaped, with only two claws. 
Superfam. C. TRIONYCHOIDEA. 
Neck bending by a sigmoid curve in a vertical plane; cervical 
vertebre without transverse processes; articulation between the 
last cervical and the first dorsal vertebra by the zygapophyses only. 
Mandible with articulary 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 hyoplastra by the A, -shaped 
entoplastron. Marginal bones absent or forming an incomplete 
series, not connected with the ribs. 
Fam. 11. Trionychide. 
