DIPNOI. 343 



concur in placing it amongst the fishes, of which it constitutes 

 the highest order. The order Dipnoi is defined by the follow- 

 ing characters : The body is fish-like in shape. There is a skull 

 with distinct cranial bones and a lower jaw, but the notochord is 

 persistent, and there are no vertebral centra, nor an occipital con- 

 dyle. The exoskeleton consists of horny, overlapping scales, having 

 the " cycloid" character. The pectoral and ventral limbs are both 

 present, but have (in Lepidosiren) the form of awl-shaped, filiform, 

 many-jointed organs, of which the former only have a membranous 

 fringe infer iorly. The ventral limbs are attached close to the anus, 

 and the pectoral arch has a clavicle ; but the scapular arch is at- 

 tached to the occiput. The hinder extremity of the body is fringed 

 by a vertical median fin. The heart has two auricles and one ventri- 

 cle. The respiratory organs are twofold, consisting on the one hand 

 of free filamentous gills contained in a branchial chamber, which 

 opens externally by a single vertical gill-slit ; and on the other 

 hand of true lungs in the form of a double cellular air-bladder, 

 communicating with the oesophagus by means of an air-duct or 

 trachea. The branchicz are supported upon branchial arches, but 

 these are not connected with the hyoid bone ; and in some cases, at 

 any rate, rudimentary external branching exist as well. The 

 nasal sacs open posteriorly into the throat. 



P 



Fig. 306. Dipnoi. Lepidosiren annectens. 



Until lately the only known members of the order Dipnoi 

 were the Lepidosiren paradoxa of South America and the Lepi- 

 dosiren (Protopterus] annectens of Africa. No fossil also could be 

 referred with any certainty to this order. Recently, however, 

 there has been discovered a most remarkable fish in the rivers 

 of Queensland (Australia), which is almost certainly referable to 

 this order, and which throws great light upon several fossil 

 forms. The organisation of this fish is so extraordinary, and 

 its affinities with some of the extinct Ganoids are so numerous 

 and important, that it will be well to quete at some length the 

 description of it given by Dr. Albert Giinther, one of the most 

 eminent of living ichthyologists. The fish in question has 

 been named the Ceratodus Fosteri, and it is known locally as 

 the " Barramunda." It is said to attain a length of about six 



