150 



FIE8T LESSONS IW ZOOLOGY. 



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small crustaceans. It abounds in 

 the Mississippi and its larger tribu- 

 taries. 



Geologists tell us that these 

 strange, old-fashioned, plated fish 

 ■were sometimes of colossal size. 

 They lived in the sea, but probably 

 in the shoaler parts near the shore. 

 They swarmed in the retired bays, 

 estuaries, and rivers of the coal 

 period. But the type began to 

 wane and die out; many of them 

 had small mouths situated far back 

 under the head; they could not 

 resist the attacks of the sharks 

 when they ventured into deep 

 water, and the changes of the old 

 coast lines were so great and sud- 

 den that their homes underwent 

 similar changes, so that they could 

 not maintain a footing. When we 

 look at the sturgeon, one of the 

 descendants of these plated fishes, 

 we see that the mouth is very 

 small, and only adapted, for eating 

 worms and snails; it lives, to be 

 sure, a part of the year in the sea 

 among the sharks, but then it goes 

 up our large rivers in the spring 

 to spawn, and the young grow up 

 there comparatively out of danger, 

 as they feed at the bottom and 

 are protected by the great bony 

 plates which cover the more ex- 

 posed part of their bodies. 



The other living representative 

 of the old-time plated fish js the 



