138 BATRACHIA. 



articulated neural arch. The atlas exhibits a double concave facette for 

 articulation with the occipital condyles of the skull, and its small neural 

 arch is firmly fused with the centrum. The well-developed neural arches 

 of the other vertebrae are provided with a pair of zygapophyses in front 

 and behind, and a large pair of transverse processes for the support of the 

 upper articulation of the ribs. The latter are all double-headed, though 

 the two facettes are sometimes imperfectly separated. Of the shoulder- 

 girdle, only the clavicular plates are known with certainty. These are 

 externally sculptured ; the interclavicle is rhomboidal in form, and slightly 

 overlapped by the clavicles, which do not meet in the middle line. There 

 is good reason to believe that the pelvis consists of three separate elements ; 

 and the ilium is elongated, articulating with a single pair of sacral ribs. 



Transverse section of sector of Labyrinthodont Tooth (Mastodonsaurus gigantues), 

 highly magnified. U. Triassic; Wiirtemberg. a, pulp cavity; b, b', longer 

 and shorter folds of wall of tooth. (After Owen.) 



The limbs are scarcely known, and no traces of a ventral shield or other 

 dermal armour have hitherto been observed. The finest known examples 

 of Mastodonsaurus were obtained from the Upper Trias of Wiirtemberg, 

 arid are now in the Museums of Stuttgart and Tubingen. Fragments are 

 also recorded from the Trias of England and India. 



Metopias, Capitosaurus, and Trematosaurus are allied genera 

 from the Trias of Germany. The contemporaneous Cycloto- 

 saurus is peculiar in having the auditory notch closed behind 

 by the union of the external supratemporal with the prosqua- 

 mosal. 



