You have those backwards. Just FYI.

From WordNet (r) 3.0 (2006) [wn]:
atheism
  n 1: the doctrine or belief that there is no God [syn:
       {atheism}, {godlessness}] [ant: {theism}]
  2: a lack of belief in the existence of God or gods


agnosticism
  n 1: a religious orientation of doubt; a denial of ultimate
       knowledge of the existence of God; "agnosticism holds that
       you can neither prove nor disprove God's existence"
  2: the disbelief in any claims of ultimate knowledge [syn:
     {agnosticism}, {skepticism}, {scepticism}]