Smaller than the male, she is not flat at all, but deep and box-like, with a distinctly beak-like front-end. This is the business end! Her way of propagating her tiny gloccidia is to grab a curious log-perch by the nose and pump her babies out in its face, so as many of them as possible may latch on and be nourished, carried, and dispersed by the fish.
We found this video of a female Snuffbox in the very act of catching a host for her young. Just at the end, you can see the little particles puffing out from her shell. These would be 'inhaled' by the fish, and establish themselves on its gills, to be carried about for a few months, and then drop off to be free living for the rest of their lives. Other fresh water mussels have various strategies for luring their host fish, but none of them make such a forceful introduction as the Snuffbox!