THE ANIMALS OF THE PAST 



429 



group of animals represented by thousands of species. 

 Another group with a similar history, traced out wholly by 

 the study of fossils, is that of the sea-lilies or crinoids, 

 radiate animals fixed by a stalk to the bottom, in struc- 

 ture resembling starfishes and sea-urchins. By the abun- 



FIG. 251. Ammonite (Ammonites humphresianus) from the Jurassic of Europe. 

 After NICHOLSON. 



dance and variety of their remains, it is evident that at one. 

 time in the earth's history the crinoids were an important 

 and flourishing group of animals. At present, however, 

 there are but very few known living species of crinoids, and 

 these are found only in the unchanging conditions of great 

 depths in the sea. Again, the Nautilus is the only living 

 near relative of what was, in Mesozoic time, a group with 

 hosts of species, the Ammonites (Fig. 251) bearing coiled 

 shells, often very elaborately ornamented. 



340. Man. The first traces of man appear in the later geo- 

 logic epochs in the period called Tertiary. Human bones 

 have been found in caves together with those of the cave- 

 lion, cave-bear, and other extinct animals. In certain lakes 

 in Switzerland and Austria have been found remains of 

 peculiar dwellings, together with ancient fishing-hooks and 



