CLASSIFICATION 



149 



(ii.) Teleostomi ; e.g. sucli well-known Fishes as the Perch, Cod, Salmon, 

 and Herring, and also the less familiar "Ganoids," living and 

 extinct. 



(1) Crossopterygii ; e.g. Polypterus. 



(2) Chondrostei ; e.g. the Sturgeons (Acipenser). 



(3) Holostei ; e.g. the Bow-fin (Amia), and the Gar Pike 



(Lepidosteus). 



(4) Teleostei ; e.g. the Perch, Cod, Salmon, etc. 

 (iii.) Dipnoi ; e.g. Neoeeratodus, Protopterus, and Lepidosiren. 



Appendix to the Glass Pisces. 

 (i.) PalaeospondtlidaeI ; e.g. Palaeospondylus. 



(ii.) OSTRACODEEMlf. 



(1) Heterostraci ; e.g. Pteraspis. 



(2) Osteostraci ; e.g. Gephalaspis. 



(3) Anaspida ; e.g. Birkenia. 

 (iii.) AuTlARCHit ; e.g. Pterichthys. 



(lv.) Ahtheodirat ; e.g. Goccosteus, Dinichthys. 



The Fishes included in the Teleostomi were formerly arranged 

 in two groups : the Ganoidei, including the Crossopterygii, 

 Chondrostei, and the Holostei, with their numerous fossil allies ; 

 and the Teleostei. Living Ganoids agree with one another, and 

 differ from Teleosts in possessing an intestinal spiral valve and 

 a couus arteriosus. It is difficult, however, to separate the two 

 groups, inasmuch as in each group there are hving forms which 

 tend to approximate to the other ; and numerous fossil genera, 

 of whose soft parts nothing is known, are in many respects 

 intermediate between the two. The position and relationships 

 of the Palaeospondylidae, Ostracodermi, Antiarchi, and Arthro- 

 dira are very uncertain. The Palaeospondylidae have been in- 

 cluded in the Cyclostomata, or at all events have been regarded 

 as more or less closely related to that group, while the absence 

 of paired fins and the apparent want of jaws have suggested 

 that the Ostracodermi occupy an intermediate position between 

 the Cyclostomata and the Gnathostomata.'' On the other hand, 

 the Arthrodira are either regarded as an independent group of 

 Fishes, or are included amongst the Dipnoi. In the latter case, 

 the Dipnoi are divided into the Arthrodira and the Sirenoidei, 

 the last mentioned group including Neoeeratodus, Protopterus and 

 Lepidosiren, and their extinct allies. 



t Entirely extinct. ' Gadow, A Classification of Vertehrata, 1898, p. 4. 



