182 



EEPTILIA 



CLASS III 



transversely elongated bands of bone alternating with the ribs. Permian ; 

 Texas. 0. testudineus, Cope. 



Pariotichus (Ectocynodon), Isoclectes, Pantyhcs, Hypopnous, Cope. Texas. 



Family 3. Diadectidae. Cope. 



Anterior teeth obtusely conical, the other marginal teeth laterally expanded, with 

 tumid bases and inner and outer cusps of unequal height. Vomer with minute teeth. 

 Basioccipital loosely articulated. Permian. 



Empedias, Cope (Empedocles, Cope). Skull triangular, 50 cm. long. Sacrum 

 of two vertebrae ; pelvic bones fused. Permian ; Texas. 

 Diadectes, Chilonyx, Bolboden, Cope. Permian ; Texas. 



Sub-Order 2. THERIODONTA. Owen. (Cynodontia, Owen.) 



Investing bones of temporal region contracting into a single broad arcade, sometimes 

 irregularly perforated ; supratemporal vacuity large, quadrate small. External bones 

 not sculptured. Occipital condyle bilobate ; premaxillae separate; marginal teeth 

 differentiated into incisors, canines, and molars. External, nares terminal, separate, 

 or undivided; internal openings displaced backwards, owing to development of secondary 

 palate. 



The skull of Theriodonts is remarkably similar in form to that of car- 



nivorous mammals, and the 

 dentition exhibits modifica- 

 tions unusual among reptiles. 

 The mandible bites within the 

 upper jaw, and the lower 

 canines cross in front of the 

 upper as in mammals. Owing 

 to the development of a 

 secondary or false palate by 

 plates from the maxillae and 

 palatines, the opening of the 

 internal nares on the roof of 

 the mouth is displaced back- 

 ward, as in crocodiles and 

 mammals. An approach to 

 the dicondylic condition of 

 the mammalian skull is also 

 frequently observed. The 

 skeleton of the trunk and 

 limbs is imperfectly known. 



Pt 



Bo Pa 



Fig. 286. 



Galesaums planiceps, Owen. Karoo Formation; Basutoland. 

 South Africa. Skull, slightly restored, from lateral (A), palatal 

 (/-'), and superior (C) aspects, Va- A Posterior tooth, enlarged. 

 ", orbit; bo, basioccipital; eh, Posterior nares; Jr, Frontal; md, 

 Mandible ; mx, Maxilla ; N, Anterior narial opening ; na, Xasal ; 

 /in. Parietal ; prf, Prefrontal ; pt, Pterygoid (after Owen). 



Family 1. Galesauridae. 

 Lydekker. 



Palatal teeth insignificant 

 or wanting ; external narial 

 Trias. 



openings confluent or separated ; limb bones slender. 



Galesaurus, Owen (Xythosaurus, Owen), (Fig. 286). Known only by the 



