4 CHELONIA. 
Order CHELONIA. 
Cheloniens, Brongniart, Bull. Soe. Philom, ii. 1800. 
Testudinata, Oppel, Ordn. Rept. 1811. 
Quadrate bone immoyably united to cranial arches. Dorsal ribs 
single-headed, the anterior attached between two vertebrae ; body 
encased in a bony shell. A plastron formed of a small number of 
elements in addition to the clayicles. No sternum. No teeth; jaws 
covered with horny sheaths. Anal opening round or longitudinal. 
Copulatory organ present, single. 
Suborder I. ATHECZ. 
Vertebree and ribs free, separated from a bony exoskeleton. Skull 
without descending processes of the parietal bones. 
Fam. 1. Sphargide. Limbs paddle-shaped, clawless; phalanges 
without condyles. Exoskeleton consisting of numerous 
small bony plates arranged like mosaic. 
Suborder IJ. THECOPHORA. 
Dorsal vertebree and ribs immovably united and expanded into 
bony plates forming a carapace. Parietals prolonged downwards, 
forming a suture with the pterygoids, or separated from the latter 
by the interposition of the epipterygoid. : 
Superfam. A. CRYPTODIRA. 
Neck bending by a sigmoid curve in a vertical plane; cervical 
vertebrae without or with mere indications of transverse processes ; 
centrum of the last cervical articulating with the centrum of the 
first dorsal. Mandible with articulary concayities; outer border of 
tympanic cavity deeply notched; pterygoids narrow in the middle, 
in contact on the median line. Pelvis not anchylosed to the cara- 
pace and plastron. Digits with not more than three phalanges. 
Kpiplastra in contact with hyoplastra; entoplastron, if present, oval, 
rhomboidal, or T-shaped. A complete series of marginal bones, 
connected with the ribs. 
I. Digits short or moderately elongate; phalanges with condyles; 
claws four or five. Neck completely retractile. Squamosal 
bone widely separated from the parietal. 
A. Nuchal plate (bone) with costiform lateral processes, extending 
below the marginals. 
Fam. 2. Chelydride. Caudal vertebra mostly opisthoccelous ; pubic 
symphysis widely separated from ischial. 
Fam. 3. Dermatemydide. Caudal vertebre proceelous; plastral 
bones nine ; pubic symphysis widely separated from ischial. 
