While trying to answer a query from Neil on the previous post, I discovered that there was an even bigger fossil cephalopod out there than the Parapuzosia I showed you yesterday (offhand, I gave the size of Parapuzosia as 2.5 m, which is apparently not entirely correct. The actual fossil itself is around 2 m in diameter, but is missing most of the living chamber [cephalopod shells are divided into a number of successive chambers, with the actual animal only occupying the youngest chamber] - 2.5 m is an estimated size if the living chamber were intact). Cameroceras was an straight-shelled endoceratid 'nautiloid' in the early Ordovician that reached about 10 m in length, though there seems to be some uncertainty - reading between the lines, I'm guessing that we don't have an entirely intact shell for Cameroceras either, and the total size is again an estimate. But note that that length doesn't include tentacles!
The picture at the top of the post comes from here, but note that the site linked is obviously a collection of pictures taken from elsewhere (a number of them even have the unmistakeable style of Palaeos.org's own Stanton Fink) and I don't know the original source* (Update: See in the comments for the apparent original site). The larger specimen on the left is apparently Cameroceras and looks to be about the right size. The smaller specimen on the right is meant to be the closely related Endoceras - Palaeos gives a length of about four metres for this critter, so the one in the picture appears a little large. The buxom wench with the rapier is, well, a buxom wench with a rapier.
*Should the original illustrator be out there, I'll be happy to correct the link. I'll also take this as a good time to remind you all that it is Catalogue of Organism's policy that any inadvertent breaches of copyright will be immediately rectified upon notification by removing the offending item.