Ammonite

[Eng. Ammon; -ite. In Ger. ammon it; Greek ̓Αμμων (Ammōn), either an Egyptian word, or from the Gr. ἄμμος ( ammos ) = sand, and suffix -ite. "Ammon stone." Jupiter Ammon had a celebrated temple in an oasis of the Libyan desert, and was worshipped there under the form of a ram, the horns of which the fo il Ammonites were thought to resemble. Hence the genus was called by the older naturalists Cornu Ammonis, a designation altered by Bruguière into Ammonite.] A large genus of fo il chambered shells, belonging to the cla Cephalopod a, the order Tetra branch i at a, and the family Ammonitidæ. The shell is discoidal, the inner whorls more or le concealed, the septa undulated, the sutures lobed and foliated, and the siphuncle dorsal. Before geology became a science, even scientific men, and much more the unscientific, were greatly perplexed by these fo ils. They were looked on as real ram's horns, or as the curled tails of some animals, or as petrified snakes, or as convoluted marine worms or insects, or as vertebræ. The petrified snake hypothesis being a popular one, some dealers fraudulently appended heads to make the resemblance more complete. It is IMG:content-0465.png:[blocks in formation] divide the genus into sub-genera or sections; or if Ammonites be looked upon as a subfamily, then they will be elevated into genera. The following is the scheme adopted in Tate & Blake's Yorkshire Lias , pp. 267, .: A. Aptychus absent. (By aptychus is meant the operculum, cover, or lid, guarding the aperture of the shell.) Chamber short, appendage ventral. Phyl loceras (Sue ). Distribution: Trias to Cretaceous. Ex.: A. heterophyllum . Chamber short, appendage dorsal. Lyto ceras (Sue ). Trias to Cretaceous. Ex.: A. fimbria tum . Chamber 1-2 whorls. Trias. Arcestes (Sue ). Chamber short, appendage ventral, apertural margin falciform, ornaments argonaut i form. Trachyceras (Laute). Trias. B. Aptychus present: I. Aptychus undivided: 1. Horny anaptychus: Chamber 1-1 whorl, pointed ventral appendage. Arietites (Waagen). Trias and Lias. Ex.: A. Bucklundi . Chamber-1 whorl, rounded ventral appendage. Egoceras (Waagen). Trias and Lias. Ex.: A. capric or nus . Chamber whorl, long ventral appendages. A mal the us (Monf.). Trias to Cretaceous. Ex.: A. mar gar it at us . 2. Calcareous (sidetes): Shell unknown. Cretaceous. IL. Aptychus divided, calcareous: 1. Aptychus externally furrowed: Aptychus thin, chamber short, apertural margin falciform, with acute ventral appendage. Harpoceras (Waagen). Jura ic. Ex.: A. radians. Aptychus thick, chamber short, apertural margin falciform, rounded ventral appendage. Oppelia (Waagen). Jura ic and Cretaceous. Chamber short, with a groove or swelling near the aperture, margin with auricles and rounded ventral appendages. Haploceras (Zitt). Jura ic and Cretaceous. 2. Aptychus thin , granulated externally: Chamber long, apertural margin simple, or furnished with auricles. Stephanoceras (Waagen). Jura ic and Cretaceous. Ex.: A. communis. Chamber long, aperture narrowed by a furrow, simple, or furnished with auricles. Perisphinctes (Waagen). Jura ic and Creta ceo us. Chamber short, aperture simple, or furnished with auricles. Cosmoceras (Waagen). Jura ic and Cretaceous. 3. Aptychus thick , smooth, punctated exter nally : Chamber long, umbilicus large, shell with furrows, ventral appendage nasiform. Simo ceras. Tithonic. Chamber short, apertural margin generally simple. Aspidoceras (Zitt). M. and Upper Jura ic and L. Cretaceous. Dr. Oppel of Stuttgart (about A.D. 1856), Dr. Wright of Cheltenham (1860), and others, have divided the Lias into different zones, distinguished from each other by the occurrence in them of typical ammonites. The zones at present recognised are here presented in an ascending series, commencing with the oldest. Geologists quote them in such a form as this: The zone of Ammon it is plan orb is at the base of the Lower Lias, the zone of A. capric or nus in the Middle Lias, . [ZONE.] Lower Lias: A. plan orb is, A. angulatus , A. Buck land i, A. oxynotus. Middle Lias A. James on i, A. capric or nus, A. mar gar it at us, A. spin at us , A. annul at us . Upper Lias: A. serpent in us, A. communis, A. Jurensis. The following ammonites characterise the- Midford Sands: A. opal in us. Inferior Oolite A. Humphriesianus , A. Sowerbii , A. Murchisoni, A. Parkins on i. Fuller's Earth: A. gracilis. Cornbrash: A. macrocephalus. Kelloway rock: A. Kanigi, A. Callovicensis , A. sublævis . Oxford clay: A. Duncan i, A. Jasoni, A. per arm at us , A. Goliath us, A. Cord at us, A. Lambert i , A. Eugenii, A. Hectic us , A. dentatus Coral rag A. var i cost at us . Supra coralline: A. decipiens . Kim me ridge clay A. biplex , A. serratus A. mutabilis . Portland Oolite: A. giganteus . In 1868 Judd divided the Lower Neocomian (Wealden) rocks into the zones of Ammonites As tier i an us, A. Noricus , and A. Speetonensis. Lower Greensand: A. Des hayes i i . F. G. Price gives the following ammonites arranged in zones from the Upper Neocomian to the Greensand of the Gault at Folk est one:-A. mam mill at us, A. interrupt us, A. auritus var., A. Delaruei, A. lautus , A. den a rius, A. auritus, A. Beudanti , A. varicosus , A. rostratus. Grey chalk: A. Coupei, A. Man tell i, A. Rho tom a gens is, A. varians. Ammonites in the Him a lay as occur 16,200 feet above the sea,