Mel,
That's what I thought - for years - especially considering Crepidula
fornicata's habit of piling up with several females on the bottom and
several males on top.  But, when I voiced that belief on Conch-L about
a year ago, I was promptly informed that fornicata refers to the shape
of a fornix, or archway, so fornicata therefore means "arch-shaped".
I still think the other explanation is more interesting :-)
Regards,
Paul M.