OPINION.
Morris: The taxpayer contends that the facts in this appeal raise a presumption that his return for the year 1918 was filed on or before March 15, 1919, which is conclusive, in the absence of proof by the Commissioner that it was not so filed, and that, therefore, the assessment of the deficiency is barred by section 277 (a) (2) of the Revenue Act of 1924, which reads in part as follows:
The amount of income, excess-profits, and war-profits taxes imposed by * * * the Revenue Act of 1918 * * * shall be assessed within five years after the return was filed, * * *.
*41We can not agree with his contention. In our opinion tl „ statute of limitations on assessment is an affirmative defense and the burden of proving that the assessment has been barred thereby is on those seeking to avail themselves of its benefit. A return showing no tax due, for the year 1918, was filed by the taxpayer prior to the purported amended return, which was forwarded to the Commissioner July 14, 1924, but the date of filing is not stamped thereon, nor was any evidence of the date of its mailing to the collector introduced. We are, therefore, unable to determine that such return was filed more than five years prior to the mailing of the 60-day letter.