Pacific razor clams max out at around 6". Atlantic Jackknife/razor clams can get a bit longer but not by much.
I think there are related species that are frickin huge. But they aren’t particularly common, and I’m not sure where their range is. And IIRC they’re all relatively thin shelled. Its sort of a thing with that whole group of species.
And as for them being relatively small these days. When I was a kid (80’s) short razor/jackknife clams were all you’d find. Water was all fucked up and whole sections of the wetlands were dying out. Now a days 6-9" jackknife clams are relatively easy to pull from the water. In fact I ate a plate of them in Philly last week.
