Zöology; a textbook for colleges and universities . rance. The skull is very peculiar, and thevertebral column is imperfectly developed. Inthe mouth are bony grinding plates instead ofteeth, and it is through the fossilization of thesethat we know a good deal about the formerabundance of the group. Lungfishes (&) Subclass Dipneusti, or lungfishes. The skeleton, though mainly cartilaginous, shows some tend-ency toward ossification. There are manyanatomical peculiarities, but the most remark-able is that of the modification of the air blad-der into a sac with numerous cellular spaces,which funct
Zöology; a textbook for colleges and universities . rance. The skull is very peculiar, and thevertebral column is imperfectly developed. Inthe mouth are bony grinding plates instead ofteeth, and it is through the fossilization of thesethat we know a good deal about the formerabundance of the group. Lungfishes (&) Subclass Dipneusti, or lungfishes. The skeleton, though mainly cartilaginous, shows some tend-ency toward ossification. There are manyanatomical peculiarities, but the most remark-able is that of the modification of the air blad-der into a sac with numerous cellular spaces,which functions as a lung. Very young indi-viduals have long, featherlike external body is covered with scales, which super-ficially resemble those of the higher fishes,though differing in the details of structure. Itis an extraordinary thing that the scales ofSagenodus, preserved in nodules about fifteenmillion years old at Mazon Creek, Illinois, agreein almost every detail with those of Neocerato-dus, living today in the rivers of From Deans Notes on Australian LungjishFIG. 127. The Australian lungfish, Neoceratodus forsteri. - FISHES 345 The living lungfishes are the Australian Neo-ceratodus or barramunda, the Lepidosiren ofSouth America, and the Protopterus of Africa.(c) Subclass Teleostomi, or true fishes. Some include TheTeieo-the lungfishes with these; others separate out true fishesadditional subclasses for certain ancient typessurviving in few species, including in one thecurious African genus Polypterus, in another thesturgeon and the paddlefish. It is difficult todefine the Teleostomi, as they are so numerousand diverse, but the skeleton is at least partlybony ; there is only a single gill opening on eachside, leading to gill arches on which are gill fila-ments ; and there is a swim bladder, which maydisappear with age. In the higher forms, withwholly bony skeleton and stiff fin rays, the pelvicgirdle approaches the pectoral one, so that thepelvic fins m
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