30 ANLMALS OF THE PAST 



tered through the rocks were arranged. For 

 the teeth were not planted in sockets, as they 

 are in higher animals, but simply rested on the 

 jaws, from which they readily became detached 

 when decomposition set in after death. To 

 complicate matters, the teeth in different parts 

 of the jaws were often so unlike one another 

 that when found separately they would hardly 

 be suspected of having belonged to the same 

 animal. Besides teeth these fishes, for pur- 

 poses of offence and defence, were usually armed 

 with spines, sometimes of considerable size and 

 strength, and often elaborately grooved and 

 sculptured. As the soft parts perished the 

 teeth and spines were left to be scattered by 

 waves and currents, a tooth here, another there, 

 and a spine somewhere else ; so it has often 

 happened that, being found separately, two or 

 three quite different names have been given to 

 one and the same animal. Now and then some 

 specimen comes to light that escaped the 

 thousand and one accidents to which such 

 things were exposed, and that not only shows 

 the teeth and spines but the faint imprint of 

 the body and fins as well. And from such rare 



