MONOGKAPH OF THE EXISTING CRINOIDS. 



69 



Flo. 20. 



FIQ. 21. 



Fio. 22. 



Fio. 23. 



FIO. 24. 



FIO. 25. 



FIG. 26. 



FIO. 27. 



FIO. 23. 



Flos. 20-28. 20, THE DIGESTIVE TUBE AND DISK AMBULACRA OF ANTEDON BIFIDA, ILLUSTRATING A COMATCUD WITH AN ENDO- 

 CYCLIC MOUTH (ADAPTED FROM P. H. CARPENTER). 21, THE DIGESTIVE TUBE AND DISK AMBULACRA OF ONE OF THE SPECIES 

 OF THE FAMILY COMASTERID.E, ILLUSTRATING A COMATULID WITH AN EXOCYCLIC MOUTH (ADAPTED FROM P. II. CARPENTER). 

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

 ARMED ENDOCYCLIC COMATULID: THE AXIS 0-fl IS THE PRIMARY ANTEROPOSTERIOR AXIS. 23, DlAORAU SHOWING THE COM- 

 PARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND ARMS IN A TEN-ARMED ENDOCYCLIC COMATULID; THE 

 AXIS a-d IS THE PRIMARY ANTEROPOSTERIOR AXIS. 24, DIAGRAM SHOWING THE COMPARATIVE RELATIONSHIPS BETWEEN THE 

 AMBULACRA, ANAL TUBE, AND ARMS IN A TWENTY-ARMED ENDOCYCLIC COMATULID; THE AXIS tt-a IS THE PRIMARY ANTERO- 

 POSTERIOR AXIS. 25, DIAGRAM SHOWING THE COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND 



ARMS IN A TEN-ARMED EXOCYCLIC COMATULID, OH COMASTERID, IN WHICH ALL OF THE ARMS ARE PROVIDED WITH AMBULACRAL 

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

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

 EXOCYCLIC 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 fl-fl 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 EXOCYCLIC COMATULID, OR COMASTERID, IN WHICH EIGHT OF THE ARMS ARE PROVIDED 

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

 0-0 IS THE PRIMARY ANTEROPOSTERIOR, THE AXIS b-b THE SECONDARY ANTEROPOSTERIOR. 28, DIAGRAM SHOWING THE 

 COMPARATIVE RELATIONSHIPS BETWEEN THE AMBULACRA, ANAL TUBE, AND ARMS IN A TEN-ARMED EXOCYCLIC COMATULID, 

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

 AXIS 0-a IS THE PRIMARY ANTEROPOSTERIOR, THE AXIS b-b THE SECONDARY ANTEROPOSTERIOR. 



