Doc Ed:Incidentally, what does a cone seat look like? ( i bet it looks like a cone...) And what regs use em?
Yeah...
Below is a picture from Creed. You can got to this thread to read more about it:
http://www.vintagedoublehose.com/forum/viewtopic.php?t=1527
It belongs to a single stage Healthways regulator of his, but the seat also looks identical to the first stage of a Sportsways. Poseidon used a metal cone with a Nylon orifice, and even now a days I think that I have seen others with cone seats.

From Creeds description:
"The bottom row are the original Healthways internals. The top are slightly modified Conshelf internals, along with a USD Titan orifice."
Creed
I hope you don't mind, your picture was just handy.