60 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Anal tube. A fleshy conical tube, usually of considerable height, situated in one of 

 the interradial areas of the disk (the anal area) and bearing at its summit, the 

 anal opening (see figs. 15-19, p. 67, and pp. 110 [7], 111). 



Anal x. The interradial situated between the two posterior radials, distal to and 

 to the left of the radianal if that plate is present. In all the recent forms anal x 



ORAL PINNULES 

 I Br (PRIMIBRACHSl 

 CENTRO-DORSAL 



CIRRUS SOCKETS 



CIRRI 



FIG. i. LATERAL VIEW OF A SPECIMEN OF ANTEDON ADRIATICA FROM TRIESTE; FOR THE SAXE OF SIMPLICITY THE POOR ARMS 



ON THE SIDE OPPOSITE THAT FIGURED ARE OMITTED. 



is exactly like the other four interradials, and these are always present if anal x 

 is present. In the recent crinoids anal x, if persistent, gives rise to a post- 

 radial series exactly resembling those on the radials, becoming itself transformed 

 into a plate indistinguisable from a true radial. This is the cause of the forma- 

 tion of 6-rayed variants, the sixth ray being situated between the two posterior 



