MONOGRAPH OF THE EXISnNG CBINOIDS. 



69 



FiQ. 20. 



Fig. 21. 



riQ. 22. 



^^/^ 



Fig. 23. 



Fig. 24. 



Fig. 26. 



FIG. 27. 



Fig. 2S. 



Figs. 20-28.— 20, The digestive titbe and disk ambulacra of Antedon bifida, illu.strating a comatuud with an endo- 

 ctcuc mouth (adapted from p. h. carpenter). 21, the digesth'e tube and disk ambulacra of one of the spectes 



OF THE FAMILY COMASTERID.E, ILLUSTRATING A COMATULID WITH AN EXOCYCLIC MOUTH (AD.VPTED FROM P. H. CARPENTER). 

 22, DLIGRAM SHOWING THE COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND ARMS IN A FIVE- 

 ARMED ENDOCYCLIC COMATULID; THE AXIS d-d IS THE PRIMARY ANTEROPOSTERIOR AXIS. 23, DIAGRAM SHOWING THE COM- 

 PARATn'E RELATIONSHIPS BETWEE.V THE AMBULACRA, ANAL TUBE, AND ARMS IN A TEN-ARMED ENDOCTCUC COMATULID; THE 

 AXIS a-a IS THE PRIMARY ANTEROPOSTERIOR AXIS. 24, DUGRAM SHOWING THE COMPARATn'E RELATIONSHIP."! BETWEEN THE 

 AMBULACRA, ANAL TUBE, AND ARMS IN A TWENTY-ARMED ENDOCYXUC COMATUUD; THE AXIS a-a IS THE PRIMARY ANTERO- 

 POSTERIOR AXIS. 25, DLAGRAM SHOWI.VG THE COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, AN.4L TUBE, AND 

 ARMS IN A TEN-ARMED EXOCYCLIC COMATUUD, OR COMASTERID, IN WHICH ALL OF THE ARMS ARE PRONIDED WITH AMBULACRAL 

 GROOVES, AND IN WHICH THE MOUTH IS RADIAL IN POSITION; THE AXIS a-a IS THE PRIMARY ANTEROPOSTERIOR AXIS. 26, DIA- 

 GRAM SHOWING THE COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND ARMS IN A TEN-ARMED 

 EXOCYXUC COMATULID, OR COMASTERID, IN WHICH ALL OF THE ARMS ARE PROVIDED WITH AMBULACRAL GROOVES, AND IN 

 WHICH THE MOUTH IS INTERRADIAL IN POSITION; THE AXIS a-a IS THE PRIMARY ANTEROPOSTERIOR, THE AXIS b-b THE SEC- 

 ONDARY ANTEROPOSTERIOR. 27, DIAGRAM SHOWING THE COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL 

 TUBE, AND ARMS IN A TEN-ARMED EXOCYCUC COMATULID, OR COMASTERID, IN WHICH EIGHT OF THE ARMS ARE PROMDED 

 WITH AMBULACRAL GROOVES AND TWO ARE UNGROOVED, AND IN WHICH THE MOUTH IS INTERRADIAL IN POSITION; THE AXIS 

 a-a IS THE PRI5IARY ANTEROPOSTERIOR, THE AXIS b-b THE SECONDARY' ANTEROPOSTERIOR. 2S, DIAGRAM SHOWING THE 

 COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND ARMS IN A TEN-ARMED EXOCYCUC COMATUUD, 

 OR COMASTERID, IN WHICH FOUR OF THE ARMS ARE PRO\aDED WITH AMBULACRAL GROOVES AND SIX ARE UNGROOVED; THE 

 AXIS a-a IS THE PRIMARY ANTEROPOSTERIOR, THE AXIS b-b THE SECONDARY ANTEROPOSTERIOR. 



