cover Exposition Ad Covers, 1876-1904, six covers incl. no. 207 on cover with small Centennial Machinery Hall Building illustrated design on flap; three Pan-Am. Expo Covers: no. 279 on multicolor overall flag design (without flap), the other two are different multicolor designs with average 2c stamps; balance are St. Louis World's Fair covers, one is multicolor design with no. 319 tied by Expo Station machine cancel, other is Electricity Building design cover to Canada with two no. 323 (horiz. cover file fold), usual mixed condition, good-fine lot