The Era of Itwertehi'ate^ 



most important agents in the formation of tlie 

 great beds of limestone in which their fossil re- 

 mains are preserved. There are few species of 

 crinoids now living, and these are mostly con- 

 fined to limited areas of very deep water and to 

 be obtained only by means of special appliances 

 for dredging in the deep 

 sea. So for a long time 

 even the most common of 

 them {Pentacrinus caput- 

 mediisce) was very rare and 

 regarded as one of the 

 great treasures of such mu- 

 seums as chanced to pos- 

 sess a specimen. The re- 

 searches of the United 

 States Fish Commission 

 steamer Albatross, how- 

 ever, brought to light a 

 locality in the Gulf of Mexico whence many 

 examples of this beautiful radiate have been 

 obtained, and other species have been discov- 

 ered by the Albatross and by the English 

 Challenger. Still, the group of crinoids is but 



79 



modern crinoid, Penta- 

 crinus caput - medusce. 

 Much reduced. 



