34 THE VERTEBRATE SKELETON. 



Subordei (5). ACANTHOPTERYGII. 



Family Cataphracti. Dactylopterus flying gurnard. 

 Family Percidae. Perca perch. 



Order 5. DIPNOI. 

 Suborder (1). SIRENOIDEI. 

 Family Dipteridae. .Dipterus. 



Family Monopneumona. Ceratodus barramunda. 

 Family Dipneumona. Protopterus African mud-fish. 



Lepidosiren. 



Suborder (2). ARTHRODIRA. 

 Family Coccosteidae. Coccosteus. 

 Dinichthys. 



NOTE. Palaeontological research has disclosed the existence of a great 

 number of forms which seem to connect with one another almost all the 

 orders of fishes as usually recognised. Forms connecting the living 

 Ganoids with the Teleosteans have been especially numerous, so that 

 these terms Ganoid and Teleostean can hardly be any longer used in a 

 precise and scientific sense. This has rendered the subject of the classifi- 

 cation of fishes a very difficult one. Though unsuitable for adoption in 

 a work like the present, by far the most natural classification hitherto 

 proposed seems to be that of Smith Woodward 1 . He considers that the 

 course of development of fishes has followed two distinct lines, the auto- 

 stylic and hyostylic (see p. 119), and groups the various forms as follows: 



HYOSTYLIC. AUTOSTYLIC. 



Subclass 1. ELASMOBKANCHII. Subclass 3. HOLOCEPHALI. 



1. Ichthyotomi. 1. (unknown). 



2. Selachii. 2. Chimaeroidei. 



3. Acanthodii. 3. (unknown). 

 Subclass 2. TELEOSTOMI. Subclass 4. DIPNOI. 



1. Crossopterygii (Palaeozoic 1. Sirenoidei. 



and Mesozoic). 



2. Crossopterygii (Cainozoic). 2. (unknown). 



3. Actinopterygii. 3. Arthrodira. 



The primitive forms in each of these four subclasses have the fins 

 archipterygia (see p. 127). 



1 A. Smith Woodward, Catalogue of Fossil Fishes in the British 

 Museum, Part II., Introduction, p. xii. 



