A. immanis, [419], [420]

Atlas and Axis, i.e. first and second cervical vertebrae; of Cryptobranchus, [13];

of Crocodilia, [283];

of Chelonia, [283], [316];

of Sphenodon, [283], [294];

atlas fused with axis, [307]

Atoposauridae, [453]

Atractaspis, [638];

dentition, [593] n.

Atria, the thin-walled receptive parts (auricles) of the heart