272 



PHYLUM ECHINODERMATA. 



terradius downward in the figure, then in Crinoid nomenclature 

 the three radii which project upwards constitute the trivium, the 

 middle one being called anterior, while the two lower radii con- 

 stitute the bivium. Further the right posterior radius is that 

 radius of the bivium to the observer's right, the radius of the 

 trivium on the same side being the right antero-lateral radius. 

 On comparing this with the enumeration of the radii adopted in 



FIG. 188. Antedon bifida, actinal surface (from Claus). mouth, A anus. The pinnules 

 are filled with the generative products. 



this work (p. 119), it would appear that the right posterior radius 

 would correspond to radius No. II, and the left posterior radius 

 to radius No. III. Following out the same comparison the 

 right antero-lateral radius of Crinoids is No. I of our enumera- 

 tion, the anterior radius No. V, and the left antero-lateral No. IV. 

 The use of the words right and left in this orientation is the 

 exact opposite of their application in other Echinoderms.* 



* As Loven considers that the anus of Crinoids is in interradius V. I 

 (as in exocyclic Echinoids), his nomenclature of the radii of Crinoids 



