Dipnoi — Ceratodus, etc. 



19 



Cephalaspis Li/eUi, from the Old Red of Forfar, is one of the 

 most perfect of these older fishes. (See Figs. 40, 41.) 



Fig. 41. — Cephalaspis Lyelli (dorsal aspect), from the Old Red Sandstone, Glammis, 

 Forfarshire (about one-third the size of the original specimen). a, one of the 

 peculiar tesserae into which the middle layer of the shield is divided by the blood- 

 vessels (drawn natural size) ; b and c, scales from different parts of the body and tail. 



Order IV.— DIPNOI. 



The Dipnoi (Table-case 36, and portion of Wall-case 5) form a Wall-case, 

 very peculiar order, having three living representatives, namely, ^°'. 5 ' 

 Protopterus in Africa (Fig. 47), Lepidosiren in South America, and No 36 ' 

 Ceratodus in Australia (Fig. 42). 



Fig. 42.— "The Australian Mudfish," Ceratodus Forsteri (recent), Australia. 



Fig. 43.—Dipterus macrolepidotus, Sedgw. and Murch., Old Red Sandstone, Scotland. 



In these fishes the skeleton is notochordal, there are a pair of 

 ptery go-palatine teeth, and a pair of incisor-like vomerine teeth above, 

 and a third pair of teeth in the lower jaw (Fig. 44). There are two 

 pairs of nostrils, more or less within the mouth, and the air-bladder, 

 single or double, takes on the function of a lung. There is one 



