320 



HISTORICAL GEOLOGY. 



common later, i. e., in the Triassic. We will describe 



only two examples : 



The Archegosaurus (primeval saurian) (Fig.. 253) 



was an animal two to three feet long, with head and body 



much like a ganoid fish, and 

 covered with ganoid plates and 

 scales. It had probably per- 

 manent gills as well as lungs, 

 and its legs were little more 

 than legged fins, such as are 

 found in some ganoids, and 

 wholly unadapted for locomo- 

 tion on land. It was a re- 

 markable' connecting link be- 

 tween ganoid fish and laby- 

 rinthodont amphibian. 



The Dendrerpetoii (tree- 

 reptile) was so called because 

 first discovered (by Dawson) 

 in the hollow stump of a sigil- 



laria tree. It was of lizard-like form, and about two feet 



long It is a curious fact that these hollow stumps of 



FIG. 252. Section of portion of a 

 tooth of a labyrinthodont. 



FIG. 253. Archegosaurus : A, plates ; B, section of tooth. 



sigillaria filled with sandstone (Fig. 254) are very rich 

 in fossils, e. g., skeletons of amphibians, remains of in- 

 sects, and shells of land mollusca. The sigillaria tree was 

 very soft and spongy, but was covered with a hard bark. 

 We may easily picture to ourselves the conditions under 



