DIPNOI. 



259 



any other Dipnoan are found between the Jurassic and the 

 present time. 



The other sub-order includes Palaeozoic forms only. Some 

 of these present, in the heterocercality of the tail and in the 

 differentiation of the unpaired fin, features which are regarded 

 by some anatomists as more primitive than the diphycercality 

 and continuous unpaired fin of living forms. We however are 

 not inclined to attribute so much importance to these facts of 



FlG.36. Dipterus'valenciennessii. Ag. Old red sandstone, \ nat. size, restored (from Wood- 

 wardfafter Traquair). 



structure. We think on the contrary that they show merely 

 that there was considerable variability in the fins in the Palaeo- 

 zoic forms\nd the particular combination of characters possessed 

 by these organs in living Dipnoi is merely one which might 

 quite well have been found indeed is found in the Palaeozoic 

 Dipnoi. 



1. Ctenodipterini. Skull with numerous small scutes, with jugular 

 plates ; vomerine teeth have not been observed. Devonian, Carboniferous, 

 Permian. Dipterus Sedgwick and Murchison (Fig. 136). Scaumenacia, 

 with heterocercal tails and two dorsal fins and an anal ; Phaneropleuron 

 Huxley, with diphycercal tail and distinct anal fin ; Ctenodus Ag., Sageno- 

 dus Owen, Uronemus Ag., Conchopoma Kner, with diphycercal tail and 

 continuous dorsal fin. 



FIG. 137. Protopterus annectens (from Claus). 



2. Sirenoidei. Skull covered with few large scutes ; with long, single 

 dorsal fin and anal fin continuous with diphycercal tail-fin. Two vomerine 

 teeth present. Ceratodus (Epiceratodus) Ag., with one lung, rivers of 

 Queensland. Teeth of this or a closely allied genus are found in the 

 Trias and Jurassic. The Dipnoan type is then lost until it appears in the 

 three genera of the present day. C. forsteri Krefft, barramunda, rivers of 

 Queensland. Prolopterus Owen, with two lungs, swamps of tropical 

 Africa. Pr. annectens Owen. Lepidosiren Fitz., with two lungs, trop. 

 Amer. L. paradoxa Nat. 



