. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. Fi^. 201 -Different views o^Nautilus Danicus. Faxoe Limestone (Upper Cretaceous), Denmark. pears, with its involute shell, its capacious body-chamber, its simple septa between the air-chambers, and its nearly or quite central siphuncle. The majority of the chambered Cephalo- pods of the Cretaceous belong, however, to the complex and beautiful family of the Ainmonitidce, with their elaborately- folded and lobed septa and dorsally-placed siphuncle. This f
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. Fi^. 201 -Different views o^Nautilus Danicus. Faxoe Limestone (Upper Cretaceous), Denmark. pears, with its involute shell, its capacious body-chamber, its simple septa between the air-chambers, and its nearly or quite central siphuncle. The majority of the chambered Cephalo- pods of the Cretaceous belong, however, to the complex and beautiful family of the Ainmonitidce, with their elaborately- folded and lobed septa and dorsally-placed siphuncle. This family disappears w^holly at the close of the Cretaceous period ; but its approaching extinction, so far from being signalised by any slow decrease and diminution in the number of specific or generic types, seems to have been attended by the develop- ment of vv^hole series of new forms. The genus Ammonites itself, dating from the Carboniferous, has certainly passed its prime, but it is still represented by many species, and some of these attained enormous dimensions (two or three feet in diameter). The genus Aiicyloceras (fig. 202), though likewise of more ancient origin (Jurassic), is nevertheless very charac- teristic of the Cretaceous. In this genus the first portion of the shell is in the form of a flat spiral, the coils of which are not in contact; and its last portion is produced at a tangent, becoming ultimately bent back in the form of a crosier. Be- sides these pre - existent types, the Cretaceous rocks have yielded a great number of entirely new forms of the Ammoni- tidcB, which are not known in any deposits of earlier or later date. Amongst the more important of these may be men- tioned Criocems, Tiirrilites^ Scap/iites, Hamites, Ptychoceras^. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nichol
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Keywords: ., bookaut, bookcentury1800, bookdecade1870, booksubjectpaleontology
