150 EEPTILIA CLASS iii 



Mandibular rami fused in a long symphysis, which is slightly forked at its 

 toothless anterior end ; posteriorly with a single series of obtuse teeth. 

 Parietal foramen and intercentra apparently wanting. Cervical vertebrae 

 opisthocoelous ; limbs imperfectly known. Supposed Trias of Elgin, Scotland, 

 and Central India. 



Rhynchosaurus, Huxley. Smaller and with fewer teeth than the preceding ; 

 mandible toothless or with minute teeth, maxillae with a single row, and 

 palatines with' a double row of small teeth. Vertebrae amphicoelous ; ab- 

 dominal ribs well developed. Upper Trias ; Shropshire and Warwickshire. 



Family 2. Mesosauridae.^ 



Small lacertiform reptilia, with very numerous, extremely long and acicular 

 teeth in the upper and lower jaws. Vertebral centra amphicoelous, toith remnants of 

 the notochord. Cervical vertebrae vnth short hatchet -shaped ribs. Dorsal ribs 

 single-headed, very thick. Ventral ribs well developed. Tarsus with two rows of 

 small bones. Extremities with five toes. 



Mesosaurus, Gervais (Ditrochosaurus, Gtirich). Karoo formation of South 

 Africa. 



Stereosternum, Coj^e, from the Permian or Lower Trias of Brazil is possibly 

 identical with, in any case very similar to Mesosaurus. 



Family 3. Champsosauridae. 



Skull with elongated gavicd-like snout. A single series of large conical teeth 

 present on the jaw-bones and palatines, and irregidar longitudinal series of minute 

 teeth on the vomers, palatines, and pterygoids. External nares terminal and confluent. 

 Mandibidar rami suturally united at the symphysis. Only two intercentra present at 

 anterior end of the neck. Vertebral centra completely ossified, slightly biconcave, or 

 amphiplatyan, and suturally united tvith their neural arches. Cretaceous and 

 Lower Eocene. 



Champsosaurus, Cope (Simaedosaurus, Gervais). Large aquatic reptiles 

 attaining a length of 2 "5 m. Premaxillae elongated into a ga vial-like rostrum ; 

 cervical ribs short and double-headed ; abdominal ribs stout. Humerus with 

 ectepicondylar groove instead of foramen. Known by fragmentary remains 

 from the Laramie Cretaceous, and Lower Eocene of the United States, and by 

 complete skeletons from the Lower Eocene of France and Belgium. 



Family 4. Sauranodontidae. 



Small long-tailed Jihynchocephalia with edentulous jau's and beak-like rostrum. 

 Temporal fossae small, parietal foramen wanting, postorbital very large, external nares 

 undivided. Vertebrae well ossified ; second sacral rib distcdly divided ; tibdominal 

 ribs stout. Fore-limb shorter than the hind, both pentadactylate. Dermal scales 

 rectangular. Upper Jura. 



Sauranodon, Jourdan. This, the solitary genus, is known by perfect 

 skeletons from the Upper Jura of Cerin, France. S. incisivus, Jourdan, attains 

 a length of about 0'7 m. 



* Geinitz, H. B., Siir Stereostenuim tumidum, Cope (Ann. Soc. Geol. Belg. vol. XXV. his p. 35), 

 1900. — Woodn-ard, A. S., On a new specimen of Stereosternum (Geol. Mag. [4], vol. IV. p. 145), 

 1897. 



