REPTILES ABUNDANT. 65 



structure of their teeth) the name of Ldbyrinthodonts. These 

 were animals of the size of a large hog. Their footmarks, dis- 



FIG. 40. 



Foot-tracks of Labyrinthodon. 



covered alike in America and the elder continent, "bear a 

 singular resemblance to the impression that would be made by 

 the palm and expanded fingers and thumb of the human hand." 

 But it is evident that the fore extremities of the animal had 

 been, like those of the kangaroo and some other genera, much 

 smaller than the hinder, some specimens of which measure 

 eight inches by five. These reptiles present affinities to the 

 fish class, in their biconcave vertebrae and the formation and 

 arrangement of the teeth. Their nostrils, being placed near 

 the extremity of the head, indicate a partially marine habitat, 

 such an arrangement being required to enable the animal to 

 breathe while nearly altogether sunk in the water. 



Quarries of the red sandstone of this system also present an 

 abundance of footmarks attributed to tortoises, thus pointing 

 to the contemporaneous existence of a third order of reptiles 

 the Chelonia. The first examples were discovered by the Eev. 

 Dr. Duncan in the quarry of Corncockle Muir, Dumfriesshire, 

 where the slabs incline at an angle of thirty-eight degrees, and 

 the footmarks are distinctly traced up and down the slope, as 

 if, when the surfaces were those of a beach at, however, a 



F 



