*Brackets and parentheses are used (brackets in the case of whole 
Psalms, parentheses in the case of verses) to indicate Psalms and verses 
of Psalms which may be omitted.  In some instances, the entire portion 
of the Psalter assigned to a given Office has been bracketed, and 
alternative Psalmody provided.  Those who desire to recite the Psalter 
in its entirety should, in each instance, use the bracketed Psalms 
rather than the alternatives.*  

*Antiphons drawn from the Psalms themselves, or from the opening 
sentences given in the Offices, or from other passages of Scripture, may 
be used with the Psalms and biblical Canticles.  The antiphons may be 
sung or said at the beginning and end of each Psalm or Canticle, or may 
be used as refrains after each verse or group of verses.*  

*On Special Occasions, the officiant may select suitable Psalms and 
Readings.*