order vi CHELOXIA 197 



quadrate belli ml. Pterygoids /arrow in the middle, in contact only along the median 

 line, without wing-like lateral expansions, separating the quadrate and basisphenoid. 

 Pelvis not anchylosed with carapace or plastron. Digits with not more than three 

 phalanges. Epiplastra in contact with hyoplastra ; entoplastron oral, rhomboidalj or 

 T-shaped. A complete series of marginal bones, connected with the ribs. 



This sub-order comprises the majority of existing and fossil Chelonians. 

 As distinguished from Pleurodires, the head is retracted by curvature of the 

 neck in a vertical plane, and the pelvis is unconnected with the plastron. 

 The different families are conveniently grouped by Baur in four superfamilies, 

 as recognised in the sequel. 



Superfamily 1. CHELONOIDEA. Baur. 



A parieto-squamosal arch ; no foramen palatinum between palatines and maxillae; 

 articular faces between the sixth and seventh cervical vertebrae plane; nuchal with a 

 distinct process on the lower side for articulation with the neural arch of the eighth 

 cervical vertebra, and without lateral processes. One biconvex cervical vertebra. 



Family 1. Dermochelyidae. Gray. (Athecae, Cope.) 



Carapace broken up into numerous mosaic-like pieces of dermal ossification, wholly 



unconnected with the vertebrae and ribs. Epidermal shields absent. Skull without 



descending parietal processes; tern pored region completely roofed, the scpiamosal 



joining the parietal. Humerus flattened ; limbs paddle- shaped, dateless, the digits 



of the manus much elongated ; phalanges without condyles. Tertiary and Recent. 



Eosphargis, Lyd. Carapace represented by a single median row of broad 

 carinated scutes and a series of marginals on either side. Plastron probably 

 devoid of tesserae. Skull broad and flat. Eocene ; England. 



Psephophorus, v. Meyer (Macrochelys, van Beneden non Gray). Skull 

 shorter, thicker, and relatively larger than in Dermochelys ; shell completely 

 tessellated, sculptured ; scutes of the larger longitudinal row of the carapace 

 devoid of carinae. Eocene and Oligocene ; Europe. 



Dermochelys, Blv. (Sphargis, Merrem). Carapace completely, plastron in- 

 completely bony in the adult, the former with seven, the latter with five 

 keels ; plastral elements eight. Recent ; Atlantic, Pacific, and Indian Oceans. 

 In this, the largest and sole surviving member of the family, the separation 

 of the vertebral column from the carapace was deemed by Cope, Dollo, and 

 others a character of sufficient importance to warrant the establishment of a 

 group (Athecae) equal in value to the rest of the Chelonia. Baur has 

 endeavoured to prove that the mosaic-like carapace was an acquired character, 

 and that this and the following family are directly related to the Chelonidae. 



Family 2. Protostegidae. Cope. 



Carapace represented merely by a row of marginals, but the plastron eery strongly 

 dt i eloped and composed of thick ossifications. Skull with descending parietal plates. 

 Humerus with the radial process short, blunt, and approximated to the head. Creta- 

 ceous and Tertiary. 



Protostega i Cope. Descending parietal plates well developed. Carapace 

 intermediate between Dermochelyidae and Chelonidae, with several primitive 



