590 



ECniNODERMATA CRINOIDEA 



CHAP. 



Fam. 1. Hyocrinidae. — Stem long 

 and persistent ; cirri absent ; stem ossicles 

 cylindrical — ligaments uniting them not 

 specialised. Arms (five) short, but with 

 extremely long pinnules. Patina com- 

 posed of long exposed basals and a ring 

 of five spade-shaped radials. Five large 

 persistent orals. Interradials and cover- 

 ing plates present. One species {Hyocrinus 

 lethellianus, Figs. 268, 269) dredged up 

 in the Southern Pacific Ocean. 



Fig. 269. — Tegmen of Hyocrinus, viewed from above 

 after removal of the arms, x 8. (From Wyville 

 Thomson.) 



Fam. 2. Rhizocrinidae. — Stem long 

 and persistent ; cirri confined to a few 

 near the root or replaced by rooting 

 branches of the stem. Sfcem-ossicles thin 

 and pentagonal at the summit, but lower 

 down compressed, elliptical in section, 

 and united by two ligaments separated 

 by a transverse ridge for articulation. 

 nanus. X 2. (From patina composed of exposed basals and 

 a ring of five short radials. Orals large 



Fig. 268. — Hyocrinus helhel- 

 lianus. X 2. ~ 

 Wyville Thomson.) 



