AMMONITES

An extinct genus of molluscous animals which inhabited convoluted chi siphouifcrous shells, sometimes called Comua ammon is, and vulgarly snake-stones. From their affinity to the naulilites, and the known organisation of the animal of the pearly nautilus, fo il shells of this genus are referred to the Tetrabrancniate order of Cephali constitute the typical genus of the second family of that order (Ammunitida). They are characterised by their conspicuous whorls, and the marginal-external position of the siphon. They abound in the strata i.da ry formation, varying from the size of a bean to the dimensions of a coach-wheel. Their name is derived fin m semblance to the horns upon the statue of Jupiter Ammon. AMMOMTIDjE. A family of Cephalopod a, vs bered siphon i fer ous shells, characterised by Ihe septa being sinuous, with lobated margins. [s. 54]