t Salamanders and their Associates 



that the shell of a iiautilus was said to be 

 made of many chambers, divided from one 

 another by partitions. In the nautilus these 

 partitions, or septa, are simple, and the edges 

 of the divisions between them plain, but in 

 other forms the sections become more and more 

 complicated where they join, and it is these 

 species that developed so abundantly in the 

 Trias. There is very much the same difference 

 in the joining of the chambers that there would 

 be between a set of boxes simply resting one 

 on top of the other, and a set in which the 

 boxes were dovetailed together like the pieces 

 of a dissected map. 



The comparatively brief period of the world's 

 history embraced by the Permian and Trias saw 

 some remarkable changes among back-boned 

 animals, not only of our continent, but else- 

 where ; it saw the disappearance of the great 

 amphibians, and the coming of dinosaurs and 

 marine reptiles. Turtles made their first ap- 

 pearance, abroad if not here, and the strange, 

 mammal-like reptiles, the anomodonts, ran 

 their course, passed across the stage, and went 



141 



