Coal; its history and uses . re known to charac-terise several recently discoveredforms. The reversal of the patternfound in Archegosaurus is not con-stant throughout the order. SeveralGerman anatomists adduce the ven-tral armour of the Labyrinthodontsin support of their reference of theorder to the true Reptiles, and dwellupon the term naked Amphibia,commonly used in German zoology todesignate what English naturalistssimply call Amphibia, as proof of theincompatibility of such defences withthe very definition of the class. It isto be noted, however, that some fewexisting Amphibia possess rudi
Coal; its history and uses . re known to charac-terise several recently discoveredforms. The reversal of the patternfound in Archegosaurus is not con-stant throughout the order. SeveralGerman anatomists adduce the ven-tral armour of the Labyrinthodontsin support of their reference of theorder to the true Reptiles, and dwellupon the term naked Amphibia,commonly used in German zoology todesignate what English naturalistssimply call Amphibia, as proof of theincompatibility of such defences withthe very definition of the class. It isto be noted, however, that some fewexisting Amphibia possess rudimen-tary shields and scutes, whilst noexact parallel to the Labyrinthodontarmour is to be met with in anyexisting animal whatsoever. A third point of importancein the organisation of Archegosaurus is the notochordalvertebral column. The axis, prefiguring what in mostvertebrates becomes segmented and ossified into thecentra or bodies of the vertebrae, retains even in thelargest specimens of Archegosaiirus its primitive or em-. Fio. 18. Ventral ar-mour of Arche-gosaurus, 122 COAL. CHAP. IV. bryonic structure. There is thus no continuous spinalcolumn in the fossil; but the regular distances of thebony vertebral arches testify to the presence in theliving animal of a cartilaginous rod which connectedthem with each other. The occipital condyles appear tohave been similarly unossified. To prevent an unfaircomparison of these embryonic features of the Carboni-ferous Archegosaurus with the relatively adult struc-ture of the Labyrinthodonts of the Trias, it should benoticed that there are many Carboniferous Labyrinth-odonts with fally ossified vertebrse. A series of ossicles, forming as clerotic bony ring, hasbeen found in the orbit of Archegosaurus, and may beexpected to recur in other Labyrinthodonts. Such astructure is unknown in existing Amphibia; it occurs insome recent and fossil reptiles and in birds. A genus which has since proved rather common inthe Coal Measures was first dete
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlo, booksubjectcoal
