KIRENOIDEI. 63 



Dipterus (figs. 48, 49). The head is much depressed and the snout 

 obtuse. The dental plates, above and below, are triangular in shape, 

 marked with outwardly radiating ridges which are tuberculated or 

 strongly crenulated. A pair of gular plates are present. There are 

 two separate dorsal fins, opposed to the pelvic and anal fins; and the 

 tail is more or less distinctly heterocercal. The scales are invested 

 with dense, punctate enamel in their exposed portion. The genus is 

 exclusively early Devonian, the type species being D, valenciennesi, about 

 0*4 in. in length, from the Old Red Sandstone of N. Scotland. 



The acutely lobate paired fins have been observed in the 

 Devonian genera Dipterus, Phaneropleuron, and Scaumenatia, 

 but the endoskeletal supports seem to have been always too 

 slightly calcified for preservation. These genera also exhibit 

 well-developed gular plates, but none have hitherto been recog- 

 nized in the Carboniferous and Permian Ctenodus and Sagenodus. 

 It is also curious that no known example of a Palaeozoic Dipnoan 

 exhibits certain evidence of anterior teeth corresponding with 

 the so-called vomerine pair in Ceratodus (Epiceratodus). 



The dental plates named Ceratodus, identical with those of 

 the existing Barramunda of the Queensland rivers, have a very 

 wide distribution ; but they seem to be confined to rocks of 

 Triassic, Rhaetic, and Jurassic age, and are extremely rare in 

 the latter. The fossils on which the genus was founded were 

 obtained from the Rhgetic Bone-bed of Aust Cliff, near Bristol 

 (Ceratodus latissimus) ; and similar dental plates occur on the 

 same horizon in Leicestershire and Wiirtemberg. A division 

 of the Muschelkalk (Middle Trias) in Germany yields a great 

 number of plates only specifically distinct, and the Lower 

 Oolites (Jurassic) of England have furnished three diminutive 

 specimens. The Kota-Maleri Group (Triassic) of India is also 

 prolific in these fossils ; while one small species occurs in the 

 Karoo Formation (Upper Triassic or Rhaetic) of Cape Colony, 

 and another in the Upper Jurassic of Colorado. Dental plates 

 of the ordinary form, as might be expected, are sometimes 

 found in the alluvial deposits of Queensland. Only two fossils 

 hitherto discovered, however, are of value as displaying the 

 characters of the fish to which these dental plates originally 

 belonged. One is an imperfect head of Ceratodus sturi from 

 the Upper Keuper of Polzberg, near Lunz, Austria ; the other 



