. Fishes. Fishes. Subclass Dipneusti, or Lung-fishes 239 In these the jugular plate is present, as in Uronemus. Dipterus valenciennesi is the best-known European species. Dipterus nelsoni and numerous other species are found in the Chemung and other groups of Devonian rocks in America. In the CtenodontidcB the tail is diphycercal, and no jugular plates are present in the known specimens. In Ctenodus and Sa^enodus there is no jugular plate and there are no marginal teeth. The numerous species of Ctenodus and Sagenodus belong. Fig. 171.—Phaneropleuron andersoniiLuxley; restored; Devonian. (After
. Fishes. Fishes. Subclass Dipneusti, or Lung-fishes 239 In these the jugular plate is present, as in Uronemus. Dipterus valenciennesi is the best-known European species. Dipterus nelsoni and numerous other species are found in the Chemung and other groups of Devonian rocks in America. In the CtenodontidcB the tail is diphycercal, and no jugular plates are present in the known specimens. In Ctenodus and Sa^enodus there is no jugular plate and there are no marginal teeth. The numerous species of Ctenodus and Sagenodus belong. Fig. 171.—Phaneropleuron andersoniiLuxley; restored; Devonian. (After Dean.) chiefly to the Carboniferous age. Ctenodus wagneri is found in the Cleveland shale of the Ohio Devonian. Sagenodus occiden- talis, one of the many American species, belongs to the coal- measures of Illinois. As regards the succession of the Dipneusti, Dr. DoUo re- gards Dipterus as the most primitive, Scaumenacia, Uronemus, Ctenodus, Ceratodiis, Protopterus, and Lepidosiren following in order. The last-named genus he thinks marks the terminus of the group, neither Ganoids nor Amphibians being derived from any Dipnoans. Order Sirenoidei. — The living families of Dipneusti differ from these extinct types in having the cranial roof-bones re- duced in number. There are no jugular plates and no marginal teeth in the jaws. The tail is diphycercal in all, ending in a long point, and the body is covered with cycloid scales. To these forms the name Sirenoidei was applied by Johannes Miiller. Family Ceratodontidae. — The CcratodontidcB have the teeth above and below developed as triangular plates, set obliquely each with several cusps on the outer margin. Nearly all the species, representing the genera Ceratodus, Gosjordia, and Con- chopoma, are now extinct, the single genus Neoceratodns still existing in Australian rivers. Numerous fragments of Cera- todus are found in Mesozoic rocks in Europe, Colorado, and. Please note that these images are extracted from scanned page im
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