Are you sure it is a squash as opposed to a melon, cantaloupe, or similar?

Madsquopper, squash/pumpkins are notorious for crossing. Anytime two varieties in the same species (pepo with pepo, maxima with maxima, etc) are grown anywhere near each other, you get hybrids in the next generation. It may be that your seedlings were crosses, in which case you may not be able to find a perfect match. Whatever it is, it's probably edible, maybe even great, lol. Even if you don't find a match, get back to us and let us know it's eating and keeping qualities.

pump-quash???

ken

Looks a bit like a 'Moon and Stars' melon, but the cross has crossed the moon out.

tj

How's about Eight Ball Zucchini (Cucurbita pepo var. cylindrica) cross?

I really don't think it's a melon. It's a squash. Regardless whether it's an identifiable cultivar, I think madsquapper is correct that it's in the c. pepo family.

A tondo scuro di piacenza squash maybe?

I usually don't remember details of my dreams but last night I woke up dreaming that the fruit in OP was on my Armenian cucumber.

Finally figured it out. I believe this is a Kabocha squash (Japanese pumpkin). Roasted one last night; it was OK, extremely mild flavor about like a spaghetti squash. Not worth growing again given the ordinary flavor, plus it didn't produce all that many fruits for the size of the plant.

Not worth growing again given the ordinary flavor, plus it didn't produce

==>>. this is one of the reasons to plant named seed every season ...

the genetics of open pollinated seed seems to denigrate over the years ... not that they will be useless .. but crikey.. as you note.. given the space.. you could have grown something predictably tastee ...

we caution many peeps sowing seed from store brought fruit.. for the same reason ... and that can be a 5 to 10 year investment before the thing fruits ... and you find out its nondescript at best ....

ken

Good advice, but this wasn't a planned event (see my original post). Anyway, after a bit more searching it seems these need to be "cured" off the vine to improve the flavor, so I'll try that with the next one.