294 



PHYLUM ECHINODERMATA. 



being usually a radianal, and another a special anal (p. 276). U. Cambrian 

 to Permian. Other interradials are not present. 



Fam. 1. Hybocrinidae. Monocyclic, 5 high basals. The right pos- 

 terior radial compound ; the superradial small or absent, the interradial 

 (radianal) large. Arms simple unbranched, uniserial. Hybocrimis 

 Billings, Hoplocrinus Grewingk. Baerocrinus Volborth. 



FIG. 200. Cyathocrinus longimanus Aug. (from Zittel). a, calyx with arms, nat. size (after 

 Angelin). 6* arm fragment of C. ramosus Ang. from the side, c from above (showing the 

 covering plates), d, calyx cover of C. malvaceusjHsill ; e the same after removal of the 

 calyx plates which lie on the interambulacral plates (after Meek and Worthen). 



Fam. 2. Heterocrinidae. Monocyclic, 5 basals, some of the radials con- 

 sisting of 2 pieces connected by a horizontal suture. Arms uniserial, 

 branched. Heterocrinus Hall, Ihocrinus Hall, Ohiocrinus Waschsm. 



Anomalocrinidae. 



Belemnocrinidae. 



Catillocrinidae. 



Fam. 3. 

 Fam. 4. 

 Fam. 5. 

 Fam. 6. 

 Fam. 7. 



Calceocrinidae. 

 Gasterocomidae. 



Dicyclic, Infrabasals fused into a disc. 



With one interradial anal plate. Anal opening low down above the anal 

 plate and between two radials. Gasterocoma Goldf., Myrtillocrinus 

 Sandb., Nanocrinus Mull. 



Fam. 8. Cyathocrinidae. Dicyclic (Fig. 190). 1 or 2 interradials in the 



