Subclass Dipneusti, or Lung-fishes 239 
In these the jugular plate is present, asin 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 Ctenodontide the tail is diphycercal, and no jugular 
plates are present in the known specimens. In Ctenodus and 
Sagenodus there is no jugular plate and there are no marginal 
teeth: The numerous species of Ctenodus and Sagenodus belong 
Fie. 171.—Phaneropleuron andersoni Huxley; 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 I]linois. 
As regards the succession of the Dipneusti, Dr. Dollo re- 
gards Dipterus as the most primitive, Scaumenacia, Uronemus, 
Ctenodus, Ceratodus, 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 Szrenotdei was applied by Johannes 
Muller. 
Family Ceratodontide. — The Ceratodontide 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, Gosfordia, and Con- 
chopoma, are now extinct, the single genus Neoceratodus still 
existing in Australian rivers. Numerous fragments of Cera- 
todus are found in Mesozoic rocks in Europe, Colorado, and 
