That's a classic description of what, in the veteran car movement anyway, is referred to as "the De Dion type" engine. Our Sizaire has such a valve configuration although (thankfully) the inlet valve is cam operated rather than the oh-so asthmatic spring loaded flapper type "atmospheric" variety.
The Anzanis I believe came in that configuration in their early days, and it looks to me as though they came later both with and without the drill holes around the bottom of the barrel. Early racing motorcycles employed such drill holes in the quest for more performance. One wonders, however, whether the increased noise level merely produced the impression of more power. Something similar still seems to occur today, as witness the drain pipe sized exhausts fitted to so many road registered cars.
Thank you Newbs for translating "monosoupape"- most illuminating. As I said, it is a term which was primarily associated with Gnome at the time they gave up on the valve-in-crown arrangement, and in no way was I intending to suggest they were the only single valved engine. Or were they, I wonder...?:confused: