THE OLDEST AIR-BREATHERS 287 



Its teeth are of a form that may have served even for 

 vegetable food, as their sharp edges must have had considerable 

 cutting power. Another curious form of tooth appears in the 

 genus Hylerpeton. It has the points worked into oblique 

 grooves separated by sharp edges, which must have greatly 

 aided in piercing tough integument. These creatures seem to 

 have been of stout and robust build, with large limbs. Still 

 another generic type (Fritschid) is represented by a species 

 near to Hylonomus in several respects, and with long and beau- 

 tifully formed limb bones, but with the belly protected with 

 rod-like bodies instead of scales. In this respect Hylerpeton 

 is somewhat intermediate, having long and narrow scales on 

 the belly instead of the oval or roundish scales of Hylonomus. 

 All these last-mentioned forms are Microsaurians, with simple 

 teeth and well-developed ribs and limbs, and smooth cranial 

 bones. Two other species are represented by portions of 

 single skeletons too imperfect to allow them to be certainly 

 determined. 



I would emphasize here that the vertebrate animals found 

 in the erect trees are necessarily a selection from the most 

 exclusively terrestrial forms, and from the smaller species of 

 these. The numerous newt-like and serpentiform species found 

 in the shales of the coal formation could not find access to these 

 peculiar repositories, nor could the larger species of the Laby- 

 rinthodonts and their allies, even if they were in the habit of 

 occasionally prowling in the forests in search of prey, and this 

 would scarcely be likely, more especially as the waters must 

 have afforded to them much more abundant supplies of food. 

 Of the numerous species figured by Fritsch, Cope and Huxley, 

 only a few approach very near to the forms entrapped in the 

 old hollow Sigillariae, though several have characters half ba- 

 trachian and half reptilian. 



