Fishes . pair on the splenials below. Jugular platesare present, and the tail is usually distinctly heterocercal. In Phaneropleuron there is a distinct anal fin shorter thanthe very long dorsal; Phaneropleuron andersoni is known fromScotland, and Scaumenacia carta is found at Scavmienac Bayin the Upper Devonian of Canada. In Dipterus there are no marginal teeth, and the tail isheterocercal, not diphycercal, as in the other Dipnoans gener-ally. Numerous species of Dipterus occur in Devonian rocks. Subclass Dipneusti, or Lung-fishes 239 In these the jugular plate is present, as in Uronenms. Dipt
Fishes . pair on the splenials below. Jugular platesare present, and the tail is usually distinctly heterocercal. In Phaneropleuron there is a distinct anal fin shorter thanthe very long dorsal; Phaneropleuron andersoni is known fromScotland, and Scaumenacia carta is found at Scavmienac Bayin the Upper Devonian of Canada. In Dipterus there are no marginal teeth, and the tail isheterocercal, not diphycercal, as in the other Dipnoans gener-ally. Numerous species of Dipterus occur in Devonian rocks. Subclass Dipneusti, or Lung-fishes 239 In these the jugular plate is present, as in Uronenms. Dipterusvalenciennesi is the best-known European species. Dipterusnelsoni and numerous other species are found in the Chemungand other groups of Devonian rocks in America. In the Ctenodontidcs the tail is diphycercal, and no jugularplates are present in the known specimens. In Ctenodus andSagenodiis there is no jugular plate and there are no marginalteeth; The numerous species of Ctenodus and Sagenodus belong. Fig. Ill.—Phaneropteuron anderscmiHuxley; restored; Devonian. (After Dean.) chiefly to the Carboniferous age. Ctenodus wagneri is found inthe 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. Dollo re-gards Dipterus as the most primitive, Scaumenacia, Uronenms,Ctenodus, Ceratodus, Protopterus, and Lepidosiren followingin order. The last-named genus he thinks marks the terminusof the group, neither Ganoids nor Amphibians being derivedfrom any Dipnoans. Order Sirenoidei. — The living families of Dipneusti differfrom these extinct types in having the cranial roof-bones re-duced in number. There are no jugular plates and no marginalteeth in the jaws. The tail is diphycercal in all, ending in along point, and the body is covered with cycloid scales. Tothese forms the name Sirenoidei was applied by JohannesMuller. Family Ceratodontidse. — Th
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