194 



FACTS AND FANCIES. 



to believe that this entirely different contrivance 

 is as old in geological time as the chambered 

 shell of the nautiloid animals. It was, indeed, 

 in all probability, more common and adapted to 

 larger animals in the Silurian period than at 

 present. 



Another curious instance — not, so far as yet 

 known, existing at all in the modern world — is 

 that of tlie remarkable stalked star-fish de- 

 scribed by Professor Hall under the name 

 Camerocrinus^ and whose remains are found 

 in the Upper Silurian rocks. The Crinoids, 

 or feather-stars, are well-known inhabitants of 

 the seas, in both ancient and modern times ; but 

 previous to Professor Hall's discovery they 

 were known only as animals attached by flex- 

 ible stems to the sea-bottom or creeping slowly 

 by means of their radiating arms. It was not 

 suspected that any of them had committed 

 themselves to the mercy of the currents, sus- 

 pended from floats. It appears, however, Jiat 

 this was actually realized in the Upper Silurian 

 period, wheii certain animals of this group de- 

 veloped a hollow calcareous vesicle forming a 

 balloon-shaped float, from which they could 

 hang suspended in the water and float freely 

 (see Fig. 17). So far as known, this remark- 



