. Catalogue of casts of fossils, from the principal museums of Europe and America, with short descriptions and illustrations. Fossils. CEPHALOPODA. 117 Ammonitidse. This is the most remarkable family of Secondary Molluscs. Some twenty or more genera and nearly 1000 species have been identified. They range from the Devonian to the Chalk inclusive, becom- ing totally extinct at the close of the Reptilian Period. The family includes the following principal genera in the order of their appearance : Goniatites, Ammonites proper, Ancyloceras and Helicoceras, Crioceras, Toxoceras, Scaphites, Hamites,
. Catalogue of casts of fossils, from the principal museums of Europe and America, with short descriptions and illustrations. Fossils. CEPHALOPODA. 117 Ammonitidse. This is the most remarkable family of Secondary Molluscs. Some twenty or more genera and nearly 1000 species have been identified. They range from the Devonian to the Chalk inclusive, becom- ing totally extinct at the close of the Reptilian Period. The family includes the following principal genera in the order of their appearance : Goniatites, Ammonites proper, Ancyloceras and Helicoceras, Crioceras, Toxoceras, Scaphites, Hamites, Baculites and Ptychoceras, and Turri- lites. The type began in the discoidal Goniatites, culminated in the compactly coiled and elaborate Ammonites, and expired in the half un- coiled forms as Scaphites, the spiral Turrilites, and the straight Bacu- lites. This division of chambered shells is distinguished from the succeed- ing family by more varied and more highly ornamented forms, with crumpled septa, lobed sutures, and marginal siphuncle. Excepting the Goniatites, the family is peculiar to and co-extensive with, the secondary strata. Ammonites proper inhabited involute shells having undulating septa, lobed and foliated sutures, a dorsal siphuncle (ventral as regards the animal), and a small nucleus, the whorl being compact from the first. The pattern is constant in each species. The shells are most beautiful when of middle growth, the ornamental characters being less developed in the young and lost in the adult. According to D'Orbigny, the compressed specimens are males, and the inflated, females. Their fossil beaks (Rhyncholites) are claimed to have been lately discovered. The shell of the Ammonite is generally thinner and more delicate than that of the Nautilus; the partitions are conse- quently more complicated, and the ribs are adorned and strengthened with spines, tubercles and bosses. With few exceptions, those having the back keeled with a furrow on each side mark th
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectfossils, bookyear1866
