266 CRINOIDEA. 



by its dorsal cirri, it is placed in the ordinary position 

 held by the Crinoids namely, with the mouth and ven- 

 tral surface of the disc looking upwards. When creeping 

 about, on the other hand, by means of the long and flex- 



Fig. 156. Saccosoma pectinata, a free Crinoid. Jurassic. 



ible arms, the animal occupies the position held by the 

 Star-fishes and Ophiuroids namely, with the mouth and 

 ventral surface of the disc directed downwards, or towards 

 the ground. 



Having now given a general account of the structure of 

 the Crinoids, it remains to consider some of their parts in 



