ORDERS CHIMEROIDEI AND DIPNOI. 953 



of their gills in water, or by their lungs on land. In the existing 

 African Protopterus there are external branchial tufts, like those of 

 the young of the Amphibia. The structure of the pelvic girdle and 

 limbs has been already noticed in the introductory chapter on the 

 class ; but it may be observed that although the skeleton is essen- 

 tially cartilaginous, yet imperfect ossifications may occur in the 

 neural spines of the vertebrae, as well as in the ribs and fin-rays. 

 The scales may be either ganoid or cycloid. 



That this order is essentially an old one, may be inferred not 

 only from the widely scattered distribution of the three existing 

 genera, and their paucity in species, and sometimes in individuals \ 

 but also from the generalised structure of its members, and the 

 occurrence of one of the existing genera in the Trias of Europe, and 

 the reputed Permian of North America. 



Family Lepidosirenid^e. — This family is only known by two 

 existing genera, and is characterised by the persistent chondro- 

 cranium, carrying a few large membrane bones, by the cycloid scales, 



Fig. 879. — Lepidosiren paradoxa, from South America. Reduced. 

 p, Pectoral ; v, Pelvic fin. 



the absence of jugular plates, the continuous vertical fin, and the 

 narrow central axis of the paired fins, which are reduced to filaments. 

 The two genera are Lepidosiren (fig. 879) of the Amazons, in which 

 the paired fins are not fringed ; and Protopterus of the rivers of 

 tropical Africa, where those fins are furnished with fringes. There 



Fig. 880. — The Barramunda (Ceratodus Forsteri), from Queensland. Reduced. 



are two small conical vomerine teeth, and larger cuspidate teeth 

 on the palate, while the body is eel-like. 



Family Ceratodontid/E. — The genus Ceratodus (fig. 880) has 

 been generally placed in the same family as the preceding forms, with 

 which it agrees in the continuous vertical fin, the cycloid scales, the 

 absence of jugular plates, and the few cranial bones. In many 



