THE ALLIES OF THE FROG: AMPHIBIA 347 



the general heading of Paleozoic Time, or the Era of the 

 Ancient Forms of Life. The paleozoic invertebrate world 

 was peculiar in its corals, crinoids (p. 246), trilobites (p. 153), 

 brachiopods (p. 233), mollusks of the orthoceras-type (p. 193), 

 and in its insects, which were largely of those groups which 

 develop without metamorphosis. Among the vertebrates, 

 the fishes represented were sharks and rays, gar-forms and 



FIG. 174. North America after the Appalachian Revolution 

 (From Dana's Manual of Geology) 



lung-fishes. The Appalachian revolution wiped the trilobites 

 entirely out of existence ; the corals and orthoceras-forms 

 disappeared soon after, with but? few exceptions ; the brachio- 

 pods were much diminished in numbers ; and the insects 

 which developed without strongly marked metamorphosis 

 after hatching dwindled away before the rapid rise of forms 

 which underwent a complete metamorphosis. The sharks, 

 rays, gars, and lung-fishes of the era became extinct as the 

 higher bony fishes began to people the sea. 



