AMMONITES, it fossil genus of Cephalopodous Mollusea, allied to tha recent genus Nautilus:. The species are known by the old Latin name Corns Ammonia. These Comm Ammonia, Cornea el Ammon of the French, were so called from a fancied resemblance to the horns with which the hetul of Jupiter Ammon with sculptured. In the earlier times their origin was variously accounted for. Some thought them petrifactions of real rams' horns, taking the name above-mentioned in a strict and downright mntter-of-fact sense ; others thought they were the curled tails of certain tattletale; soma took them for petrified marine worma rolled up; others saw in them coiled serpents, whence they were called Snake-Stones. The legends of the saints invested them with a sacred interest.
And the prayer, we are told, was not only followed by petrifaction, but by decapitation. We believe that there is a similar tradition of St. Keyna, who, when she found herself in a wood at Keynshnin, between Bath and Bristol, surrounded by serpent; changed them by the fervour of her devotions into headless stones. Nor were these opinions con fined to the mere vulgar. Worming described Ammonites as petrified adders. Langius considered them to be either the vertebrae of serpents or convoluted marine insects. These notions were not loot on the dealers ; and there are few fossil collections which do not even now possess whet was called 'a perfect Cornu Ammonia,' that is, an Ammo nite with a carved serpent's head ingeniously fitted on to the fossil shell by way of aperture. Our limits will notpermit us to dwell on this fabulous part of the history of Ammonites further than to observe that other learned men, Torellus Sarayna, Frscaatonus, and others, considered them as luaus Naeurm, formed by the plastic power of the earth. The ancients held them in high estimation as very sacred and of the highest value to the dreamer. Thus Pliny (` Hist. Mund.; xxxvi. 10), " Hammonis cornu inter sacratissimas rhtbIopire genunae, aureo colore, arietini cornus effigiena reddens, promittitur pnedivina somnia representare ;" and even to the present time the Indians tub said to ascribe extraordinary properties to them.
To the zoologist Ammonites are objects of great interest, and to the geologist they are of the utmost consequence. " It is eamy," says Mr. Phillips, in his Guide to Geology' (8vo. 1834), "to see how important, in questions concerning the relative antiquity of stratified rocks, is a knowledge of .A mmonites, since whole sections of them aro characteristic of certain systems of rocks." (sec. 82.) Dr. Buckland (` Bridgewater Treatise,' p. 333), thus comprehensively describes the range of these extinct cephalopodous mollusks : "The family of Ammonites extends through the entire series of the fossiliferous formations, from the transition strata to the chalk inclusive." According to Mr. Owen's system, the Ammonites farm the fourth genus of his second family (Ammonitithe) of his first order Tetra bronchiolar., of the class Cep/is/epode. In the opinion of all natu ralists this great group of fossils requires to be subdivided. The GonialitestOloNteverEs] of the Paleozoic rocks have been effectually separated; tire Ceralites of the triassie strata may he also withdrawn, but still the number of genuine Ammonites which remain is too enormous to be treated except in sections more or less founded on structural affinities. Without discussing what may be the best principles for such a classification, we may refer to that of You Buch, as moat generally accepted by geologists. This is mainly founded en a consideration of the sutures, or sinuous lines at the surface of the shell, formed by the edges of the diaphaagunah plates which separate the chambers.
To illustrate this view of the subject we subjoin a few examples of characteristic Amnionitie sutures.
The following are Von Buch's groups, with their prevalent geological distribution :— A rietes.—The back is usually broad, aud carinated (often a furrow on each side of the keel) ; the ribs are simple and strong. The sutural line formed upon the following general model :— The group of Arida, including A. Bucklandi, A. Conybeari, &e., belongs almost wholly to the Lias formation.