Yes Dave you're right of course, it is
M. gracilis (I did say I wasn't certain

). I've been away too long.
Little change otherwise Doug, your new cactus will still produce a large multiheaded plant in no time.
Dave - I was never really a Mamm collector, I was mainly into Gymnos, Notos/Parodias, Echinocereus, Copiapoa, Neoporteria, Astrophytums, Ariocarpus, Frailias and Turbinicarpus. I kept other genera of course including a lot of monotypic species (or almost mono like Lophophora for example). I also like the small-bodied, large-flowered Mamms.
Always dreamed of building a collection of the more demanding genera, such as Melos, Discos and Uebelmannias, but apart from the odd plant that overwintered in the conservatory I left it at just reading and dreaming
Bruce