I'd forgotten the incident, but it does sound very familiar now that someone has brought it up. But I still don't remember the context at all.
So of course, I promptly googled "assume cylindrical sharks," and here was the first hit:
Kitefin Shark - Dalatias licha WHAT TO LOOK FORSo apparently cylindrical sharks are for real! Who knew? (Certainly not me -- I took physics, chemistry and engineering classes in college. No biology.)
This is a medium-sized cylindrical shark with a short, blunt snout, and thick, fringed lips. Its spineless dorsal fins originate behind the pectoral fin rear tips, with the base closer to the pectoral than the pelvic fin bases; the second dorsal fin is larger. It has a weak ventral caudal fin lobe, and most of the posterior margins of its fins are translucent.