chiasmus

chi·as·mus  [kahy-az-muhs]  noun, plural chi·as·mi  [-mahy]
a reversal in the order of words in two otherwise parallel phrases, as in “He went to the country, to the town went she.”   http://dictionary.reference.com/browse/chiasmus

The Concise Oxford Dictionary of Literary Terms by Chris Baldick provides a more extensive description:

chiasmus [ky-AZ-mus] (plural -mi), a figure of speech by which the order of the terms in the first of two parallel clauses is reversed in the second. This may involve a repetition of the same words ("Pleasure's a sin, and sometimes sin's a pleasure" —Byron) or just a reversed parallel between two corresponding pairs of ideas … . The figure is especially common in 18th century English poetry, but is also found in prose of all periods. It is named after the Greek letter chi (x), indicating a "criss-cross" arrangement of terms. Adjective: chiastic.

An example is Matthew 23: 11-12.

            A.  "Whoever exalts himself 

                     B.  will be humbled,
                     B'.  and whoever humbles himself 

            A'.  will be exalted."

 Another good example comes from Genesis 9:6:

A.   Whoever sheds
  B.   the blood
    C.     of man
    C'.     by man shall
  B'.   his blood
A'.   be shed

 http://www.drmardy.com/chiasmus/welcome.shtml 

 Another example is Proverbs 10:3-4.

          A.  Treasures of wickedness profit nothing, 

                    B.  But righteousness delivers from death.

                    B'.  The Lord will not allow the righteous soul to famish, 

          A'.  But He casts away the desire of the wicked.