TYPE ECHINODERMA. 



541 



I. CLASS CRINOIDEA. 



The Crinoids, or Sea-lilies (Fig. 249), constitute a group of 

 forms which iu the earlier geological periods reached a high 

 grade of development, but to-day the class is represented by 

 comparatively few forms, for the most part confined to deep 



FlG. 249. Pentiicrinus maclearanus (after WYVILLE THOMPSON from HERTWIG). 



water. One of the most characteristic features of the group 

 is the presence of a more or less elongated cylindrical stalk, 

 one end of which is attached to stones or other objects which 

 serve as supports for the animal, while at the other end is 

 the body proper, which has a more or less cuplike form. In 

 the peculiar genus Hotopus the stalk is thick and short, and 

 may be described rather as the prolonged apex of the body 



