I cut open the fruit, finding it mostly, but not completely mature. The seeds popped out pretty easily--there wasn't much membrane. What was there smelled a bit like squash. From what I've been able to tell, when the fruit is completely ripe the inside literally falls apart, and when it is a bit less ripe the inside has a greenish hue. It appears that they sometimes cook the entire fruit at the immature stage, after peeling the outside off, and the membranes around the seeds contain their own unique flavors.
Since these were mature enough to have a hard woody shell, I peeled the somewhat air filled membranes off, turning my fingers purple in the process. I was surprised how much pigment there was, as I know from my previously collected seed that the purple color completely disappears within a day or two of the seed floating to the surface, and the membrane completely rots away within the week.
Here you can see that the color (and size) of these seeds is different from that of a recent batch that I collected from a ruptured pod.
I couldn't find any obvious way to get the shell off. Finally I resorted to a nut cracker which easily split the membrane, but also the nut inside, which is crumbly and tends to disintegrate when handled. The shell actually adheres to the inside, making it impossible to get off without reducing the inside to fragments.
My research about what to do about this has been unfruitful, but I'll look some more. I'll probably also try to pick a couple less mature, as I understand the shell is soft removable by hand. I wonder if this green seed is viable? I should probably set some aside to try germinating. I'm keeping them in clean water for now.