DIPNOI 



255 



TRIBE 1. 



Family PHANEROPLEURIDAE. With a diphy cereal, or very slightly 

 heterocercal tail. The anal fin is separate in Phaneropleuron, and in 

 Scaumenacia there are two 

 dorsal fins as well (Fig. 227). 

 There are large paired parietals 

 and frontals. The median 

 cranial bones are little de- 

 veloped (Fig. 208). Two large 

 inferior jugular plates are 

 present. The scales are thin, 

 with bone-cells, and are covered 

 with spinelets as in Ceratodus 

 (Fig. 201). The dermal fin- 

 rays are strong and bony in 

 this and the next two families. 

 The teeth have tnberculated 

 ridges (Huxley [227-8], Miall 

 [299],Whiteaves [488], Jaekel 

 [237], Traquair [459, 462]). 



Phaneropleuron, Huxley ; 

 Upper Old Red Sandstone, 

 Scotland ; Devonian, Canada. 

 Scaumenacia, Traquair ; De- 

 vonian, Canada. 



Family URONEMIDAE. The median fins are continuous, and the tail 

 is diphycercal (Fig. 227). The palatine and splenial groups of teeth are 

 not fused into dentary plates. The cranial bones are numerous, and 



Fio. 225. 



Dorsal view of the lower jaw of Dipterus. a, 

 articular ; an, angular ; d t dentary ; sp, splenial tooth 

 on the splenial bone. 



' cf. 



'of. 



FIG. 226. 



Dipterus Valendennesii, Sedgw., restored. (After Traquair, slightly modified.) o.il.f, anterior 

 dorsal tin ; a.f, anal fin ; c.f, caudal fin 1 ; op, operculum ; p.f, pectoral fin ; pv, pelvic fin. 



disposed as in Dipterus ; the presence of gular plates is doubtful. The 

 scales are thin (Traquair [458]). 



In the continuity of the median fins and the simple condition of the 

 teeth these fossils are perhaps the most primitive Dipnoi known. In the 



