Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Fig. 577. a Septum. The number of chambers is irregu- lar, and they are generally wanting in the in- nermost whorl. The animal of the recent Tur- ritella communis partitions off in like manner as it advances in age a part of its spire, forming a shelly septum. Nearly twenty species of the genus Bellero- Belierophon costatus, Sow. phon (see fig. ), a shell without chambers Mountain Limestone. vi ' ' i⢠â a j
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Fig. 577. a Septum. The number of chambers is irregu- lar, and they are generally wanting in the in- nermost whorl. The animal of the recent Tur- ritella communis partitions off in like manner as it advances in age a part of its spire, forming a shelly septum. Nearly twenty species of the genus Bellero- Belierophon costatus, Sow. phon (see fig. ), a shell without chambers Mountain Limestone. vi ' ' i⢠â a j. * ± ⢠like the living Argonaut, occur in the Mountain Limestone. The genus is not met with in strata of later date. It is most generally regarded as belonging to the Heteropoda, and allied to the Glass-Shell, Carinaria ; but by some few it is thought to be a simple form of Cephalopod. The carboniferous Cephalopoda do not depart so widely from the living type (the Nautilus) as do the more ancient Silurian representa- tives of the same order; yet they offer some remarkable forms scarcely known in strata newer than the coal. Among these is Orthoceras, a siphuncled and chambered shell, like a Nautilus un- coiled and straightened (fig. 578). Some species of this genus are Portion of Orthooeras laterals, Phillips. Mountain Limestone. several feet long. The Goniatite is another genus, nearly allied to the Ammonite, from which it differs in having the lobes of the septa free from lateral denticulations, or crenatures ; so that the outline of these is continuous and uninterrupted. Fig. 579. Fig. 580.
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