The Diestoceratidae were a family of cyrtoconic oncocerids from the Middle to Upper Ordovician with a characteristic cross-section.
Characters (from Sweet 1964): Compressed, straight to slightly endogastric brevicones. Siphuncle marginal, cyrtochoanitic with discrete, irregular actinosiphonate deposits.
[S64] Sweet, W. C. 1964. Nautiloidea – Oncocerida. In Treatise on Invertebrate Paleontology pt. K. Mollusca 3. Cephalopoda – General Features – Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea (R. C. Moore, ed.) pp. K277-K319. The Geological Society of America and the University of Kansas Press.
Christopher 00:16, 16 January 2011 (UTC)