THE rR( TOROSAURIA. I95 



another down to tlie bone in such a way, that the mandibular 

 teeth are ground to an edge, while the maxillary and palatine 

 teeth are w^orn upon their inner and outer faces respectively. 

 The extinct Lizards of the Triassic age, HhyncliosauTus and 

 Syperodapedon^ appear to have been very closely allied to 

 Sphenodon. 



3. The Homoeosauria. — The remains of Lizards of small 

 size, and agreeing in the most important points of their osteol- 

 ogy with the ordinary Lacertilia^ but having amphicoelous ver- 

 tebrae, have been found in the older Mesozoic rocks, from the 

 Solenhofen slates to the Trias inclusively. They cannot be 

 identified with either the Rhynchocepliala., or the Ascalahota^ 

 and may be provisionally grouped as Homoeosauria, The 

 genera Somoeosaurus^ Sap>hoeosaurus^ and Telerpeton^ belong 

 to this group. 



4. The Protorosauria. — These are the oldest known Sau- 

 ropsida, their remains occurring in the Kupferschiefer of 

 Thuringia, wdiich is a part of the Permian formation, and in 

 rocks of corresponding age in this country ; but no more mod- 

 ern representatives of this group are known. 



The Thuringian Lizard [Protorosaurus) does not appear to 

 liave attained a length of more than six or seven feet. The 

 neck is remarkably long, the cervical region being equal to the 

 dorsal in length, and it bears a skull of moderate size. The 

 tail is long and slender, and the limbs w^ell developed, as in 

 the existing Monitors. Notwithstanding the length of the 

 neck, it contained not more than nine, possibly not more than 

 seven, vertebrae, which, except the atlas, are remarkably stout 

 and strong. There are about eighteen or nineteen dorsal, two 

 (or not more than three) sacral, and more than thirty caudal 

 vertebrae. In all these vertebrae the neurocentral suture is 

 completely obliterated, and the centra are slightly concave at 

 each end. The side of each cervical vertebra, after the atlas, 

 presents, near its anterior edge, a small tubercle, with which 

 the head of a slender styliform rib articulates. The transverse 

 processes of the dorsal vertebrae are very short, antero-posteri- 

 orly flattened, plates, and the strong ribs are articulated with 

 them by undivided heads. The sternum has not been pre- 

 served. In the abdominal region of some specimens, numerous 

 short and filiform bones appear to represent, and correspond 

 with, the abdominal ribs of Plesiosauria and Crocodilia, 



The spinous processes of the caudal vertebrae, up to nea/ 



