Brilliant, thanks ladies. I’m sure you’re right about it being a Psammina. I had, of course, binned the slide, and have just spent the last hour fruitlessly cutting at the specimen to try to find more.
I cannot see any septation in my photos. I followed the key as you suggested, Maxine, which got me fairly securely to Psammina simplex, though I really wish I had more material to recheck. Put it down to experience.