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beaver. When it lived, the place now occupied by the great plains was 

 a shallow, tropical sea, five hundred miles wide, and no one yet knows 

 how long. It swarmed with fishes, and on these forms, loon-like, the 

 Hesperomis doubtless fed. What a strange creature it must have been, 

 with its long snake-like neck terminating in a head and jaws like those of 

 a lizard ! 



Fig. 3G5. — A bird with teeth {Hesperomis). 



Ostriches. 



Strange creatures are the ostriches and their allies. Indeed, they are to 

 be regarded as almost as •old-fashioned' as the forms just mentioned. 

 Almost all of their relatives lived in the past, and the few remaining forms 

 seem greatly out of place among the birds of to-day. Yet still they 

 linger in the southern hemisphere, and from present appearances it will 

 probably be a long time before they "all become extinct. 



