Slinky black viscose spandex dress in jet-black from Leifnotes from Anthropologie (rn#66170).  Tiered with ruched ruffles and elastic shirring, and a draped bodycon mini skirt, this has one wide shoulder strap and two thin strappy ones on the other side.  

Size S - chest around armpits is about 29" UNstretched, and length from neck to hem is about 30" (slightly assymetrical).  

Excellent condition with no stains, holes, fading, pilling, or signs of wear-and-tear...smoke-free home too!