. CLASSIFICATION 149 
(ii.) TELEOsTOMI ; e.g. such well-known Fishes as the Perch, Cod, Salmon, 
and Herring, and also the less familiar “Ganoids,’ living and 
extinct. 
(1) Crossopterygil ; e.g. Polypterus. 
(2) Chondrostei ; eg. the Sturgeons (Acipenser). 
(3) Holostei; eg. the Bow-fin (Ama), and the Gar Pike 
(Lepidosteus). 
(4) Teleostei ; eg. the Perch, Cod, Salmon, ete. 
(iii.) Drpnor; e.g. Neoceratodus, Protopterus, and Lepidosiren. 
Appendix to the Class Pisces. 
(i) PALAEOSPONDYLIDABT ; e.g. Palacospondylus. 
(ii.) OstTRACODERMTT}. 
(1) Heterostraci ; e.g. Pteraspis. 
(2) Osteostraci ; e.g. Cephalaspis. 
(3) Anaspida; eg. Birkenia. 
iii.) ANTIARCHIT ; e.g. Pterichthys. 
(iv.) ARTHRODIRAT ; e.g. Coccosteus, Dinichthys. 
The Fishes included in the Teleostomi were formerly arranged 
in two groups: the Ganoidei, including the Crossopteryegii, 
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 conus arteriosus. It is difficult, however, to separate the two 
groups, inasmuch as in each group there are living 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 Neoceratodus, Protopterus and 
Lepidosiren, and their extinct allies. 
+ Entirely extinct. 1 Gadow, A Classification of Vertebrata, 1898, p. 4. 
