From the seller:
A very elegant 1865-1870 ivory silk dress. The bodice is decorated with thin bands of lilac silk trim. The bodice has a center back peplum and flared sleeve cuffs. The armscyes are piped. The bodice is lined with cotton and has a front hook and loop closure. The lilac silk buttons are decorative. The skirt hemline is decorated with lilac satin trim. The skirt is fully lined with cotton. The dress is in good display condition. There is a 3 inch stress break near the back neckline, a 2 inch stress break and areas of stress near the waist band that is covered by the bodice. (See photos.) There is a ½ stress break in the skirt and one dime size hole. A very pretty display dress. Bust 32 Waist 24 Front skirt length 37 Back length 41 Width at hemline 126.
I think, based on the sleeve style, the fullness of the skirt, the waistline, and the back details of the bodice, this is a seaside outfit from about 1864/1865. The lavender dress in the fashion plate below (1864) has a very similar cut.