AMMONITES

An extinct genus of molluscous animals which inhabited convoluted chambered siphon i fer ous shells, sometimes called Cornua ammon is, and vulgarly snake-stones. From their affinity to the nautili tes, and the known organisation of the animal of the pearly nautilus, fo il shells of this genus are referred to the Tetrabranchiate order of Cephalopods, and constitute the typical genus of the second family of that order (Ammonttidce). They are characterised by their conspicuous whorls, and the marginal-external position of the siphon. They abound in the strata of the secondary formation, varying from the size of a bean to the dimensions of a coach wheel. Their name is derived from their resemblance to the horns upon the statue of Jupiter Ammon. AMMONITID^. A family of Cephalopods, with chambered syphon i fer ous shells, characterised by the septa being sinuous, with lobated margins. [s. 53]