STRUCTURE OF CRINOIDS. 



185 



from one hundred to 

 one thousand fathoms 

 in the North Atlantic 

 and Floridan seas, 

 and is a characteristic 

 member of the abyssal 

 fauna. This crinoid' 

 consists of a jointed 

 stalk, a cup -shaped 

 body (calyx), from 

 the edge of which 

 from five to seven 

 (the number varies) 

 arms (brachia) radi- 

 ate, which subdivide 

 into a double alter- 

 nate series of pin- 

 nules. The mouth is 

 situated in the centre, 

 while the anus is situ- 

 ated on a conical pro- 

 jection on one side of 

 the oral disk, between 

 the bases of two of 

 the arms. R. Raw- 

 soni Pourtales occurs 

 in from eighty to one 

 hundred and twenty 

 fathoms at Barba- 

 does. 



In Holopus, a short, 

 stout form with no 

 true stalk, but at- 

 tached by abroad en- 

 crusting base, there 

 -are ten arms originat- 

 ing from five axial 

 joints. " When con- 



-i ,1 

 tracted the arms are 



Fig. 128. Rhizocrtnits lofoffnsis Sars. twice natural 

 lzefJ- After Wyville Thompson. 



