II.—A Short Account of the Ammonites and their Allies, as Exhibited in the Cephalopod Gallery at the British Museum (Natural History)

Extract

The great group of the Ammonites (using that term in its general acceptation) is distinguished from all other kinds of chambered shells of the Cephalopod type by the complicated foliations of the margins (sutures) of the partition walls or septa into which such shells are subdivided. Though typically coiled, much in the manner of the flat pond-snail, Planorbis, there are straight and variously curved Ammonites; but all have the common character of a highly foliated “suture-line.”