I'm partial to the convention that has become common in recent SRFIs:

srfi-${N}/srfi/${N}.sld

It's concise and clear.

Often, authors put tests at the srfi-${N}/ level, e.g. at srfi-${N}/srfi-${N}-test.scm. I'd rather see them under the srfi directory, without a "srfi-" prefix, e.g. at srfi-${N}/srfi/${N}-test.scm. I don't think that should cause problems with loading the tests when they're not needed.

What do people think of that convention?