254 



BEAKED LIZARDS. 



Allied Families. 



development down the tail ; while inferiorly there are large squarish scales arranged 

 in transverse rows. Attaining a length of about 20 inches, the tuatera is olive or 

 blackish in ground-colour, upon which are small yellowish dots, while the lobes of 

 the crest on the neck and back are likewise of the latter colour. The perforation 

 in the parietal bones of the skull just referred to covers a rudimentary eye, which 

 although now functionless was probably a working organ in the ancestors of 

 the Vertebrates. In the young tuatera this pineal eye can be seen through the 

 translucent skin, but in the adult this skin becomes opaque. 



In the Jurassic rocks of Europe there occur remains of reptiles 

 allied to the tuatera, but constituting a distinct family (Homceosaur- 



idce) typically represented by the genus 

 HoincBOsawrus. These have no tusk-like 

 teeth in the front of the jaws, and the lower 

 end of the humerus has a perforation only 

 on its inner side, and there are no inter- 

 centra between the vertebrae of the back, 

 and no hook-like processes to the ribs. A 

 third family (Rhynchosauridce) is typified 

 by the genus Rhynchosaurus, from the Trias 

 or New Red Sandstone of England, and is 

 characterised by the beak being toothless 

 and probably sheathed in horn ; the palate 

 having two or more longitudinal rows of 

 teeth separated by a groove. From the 

 preceding families these reptiles differ by 

 having only a single aperture to the nostrils, 

 and by the bony union of the two branches 

 of the lower jaw ; while the articular 

 surfaces of the vertebrae are nearly flat. 

 Moreover, there is no vacuity in the middle 

 skull of the Hyperodapedon (J nat. size). f the top of the skull. In the typical genus 

 The upper figure shows the superior aspect ; the there is a single row of teeth on the inner 



lower one on the left the palate, and the right lower . -, e , , - i j. i 



one the under surface of the front of the lower jaw. Slde of the g r00ve on the P alate > but m 



Hyperodapedon, there were numerous rows, 

 as is shown in the illustration. The extremity of the beak in each jaw formed 

 two curved tusk-like processes, which diverged in the lower one. 



The Permian rocks of Europe yield remains of genera, such as 

 Proterosaurus and Palceohatteria, differing markedly from the fore- 

 going, and constituting a second suborder (Proterosauria), characterised by the 

 complex nature of the bones forming the shield on the lower surface of the body, 

 by the fifth metatarsal bone of the hind-foot being of an ordinary type, and like- 

 wise by the lower bones of the pelvis being expanded into large flattened plates, 

 instead of comparatively narrow. The last feature allies the group to the earlier 

 Sauropterygians. In the genus first named the vertebrae of the neck have cup- 

 shaped articular surfaces behind and balls in front, and there are no intercentra 

 between the vertebrae of the back, but in the other the articular surfaces of the 



Oldest Types. 



