If consent to the application of the provisions of section 2513 is signified as provided in Sec. 25.2513-2, and not revoked as provided in Sec. 25.2513-3, the liability with respect to the entire gift tax of each spouse for such ``calendar period'' (as defined in Sec. 25.2502-1(c)(1)) is joint and several. See paragraph (d) of Sec. 25.2511-1. [T.D. 7238, 37 FR 28730, Dec. 29, 1972, as amended by T.D. 7910, 48 FR 40375, Sept. 7, 1983]