APPEARANCE OF VERTEBRATE ANIMALS. 123 



Unlike ordinary fishes, they have lungs as well as gills, and 

 their mouths are armed with sharp, bony, beak-like teeth (Fig. 

 115), with which they can inflict terrible bites on the small 

 fishes and frogs which furnish them with food. Their most 

 remarkable habit is that of burying themselves in the mud of 

 dried-up ponds, forming around themselves a sort of water- 

 chamber or "cocoon," in which they remain in a torpid state 

 until the return of the rainy season sets them free. 



Another example of these Dipnoi is the Barramunda, or 

 Ceratodiis of the Australian rivers (Fig. 108^). This fish re- 

 sembles the Lepidosiren in many essential points of structure ; 



KiG. 109. — Anterior part of the palate of Dtptertis. Showing the dental plates ut a. 



Devonian. — After Traquair 



but its fins have lateral rays, and are consequently of some 

 breadth, though of peculiar form, and its mouth is armed 

 with flat, pavement-like teeth, wherewith it browses on aquatic 

 grasses. 



These modern fishes have enabled us to understand several 

 mysterious forms met with in the older rocks. In the first 

 place, they show the meaning of certain flat-toothed fishes, like 

 Dtptertis of the Devonian (Fig. 109), Conchodus of the Car- 

 boniferous (Fig. no), and Ceratodiis of the Carboniferous and 

 Trias (Figs, iii, 112), previously of very doubtful character. 

 Tlxese must all have been of similar structure and habits with 



