114 AMPHIBIA CLASS II 



graph of 1873, Sauvage describes 52 species from Licata, and of these 44 are 

 of marine origin. The character of this fish fauna is essentially Mediterranean, 

 but without exception the species are extinct. So far as fishes are concerned, 

 there is scarcely any noteworthy difference between the Pliocene fauna and 

 that of the present day. 



The distribution of fishes in time affords many facts illustrating the 

 development of this class. In the Palaeozoic epoch there were only Selachii, 

 Holocephali, Dipnoi, Ostracodermi, and Ganoidei ; the Selachii and Ganoidei, 

 indeed, appearing together in the Silurian. These two main divisions of the 

 phylum of fishes must thus have become separated very early, if indeed they 

 originated from a common stock. 



Fossils beginning in the Old Red Sandstone, and ranging through all 

 later formations, prove that the Holocephali had already diverged from the 

 Selachii in Palaeozoic times, and the branch has been preserved with its 

 partially embryonic characters (polyspondyly, autostyly) until the present day. 



The origin of the Dipnoi is quite obscure. Their Palaeozoic representa- 

 tives agree in many respects with the Crossopterygii. As, moreover, the 

 Dipnoi also share important characters with the Holocephali, it seems probable 

 that the Holocephali, Dipnoi, and Ganoidei arose from a common stock. 



So far as the development of the internal skeleton is concerned, the 

 Osti"acodermi and Arthrodira are quite primitive. Their origin is wholly 

 unknown. Among the Ganoids the Crossopterygii form an isolated group, 

 well separated from the other orders both phylogenetically and systematically, 

 having its last survivors in the modern Polypteridae, and probably more closely 

 related to the Dipnoi and Amphibia than to the other Ganoids. The Hetero- 

 cerci, Lepidostei, and Amioidei form a closely connected group of Ganoids. 

 It has already been remarked that the first order not only precedes the 

 Lepidostei in time, but is also probably ancestral to them. The Amioids may 

 have diverged from the Lepidostei during the Triassic or Jurassic period. 



The Teleosteans are merely a great lateral branch of the Ganoids. It is, 

 however, improbable that they are of monophyletic origin ; for although the 

 Clupeoids are the ancestral group of most of the Physostomi, which have 

 arisen from the Mesozoic Amioids, other families even on their first appearance 

 seem to be so remotely allied to Clupeoids that a different origin must be 

 sought for them. The Physoclysti are indeed only derivations of the Physo- 

 stomi differentiated in various directions. 



[Tlie section Pisces has been translated and revised by Dr. Arthur Smith Woodward, of 

 the British Museum, wlio has attempted to bring the subject up to date, while preserving in 

 the main the author's methods and principles of classification. — Ed.] 



Class 2. AMPHIBIA. Auiphibians and Batracliians.i 



Cold-blooded vertebrates, aquatic or terrestrial in habit, usually naked, hut some- 

 times toith a corneous or osseous dermal covering ; resjnration both branchial and 

 pidmonari/ in early stages, and in some forms gills remain functional throughout life. 

 Development by metamorphosis, but without amnion ami allantois. Skull with two 

 occipital condyles. Bibs never attached to sternum. Limbs adapted for ambulation 

 or natation, never in the form of fins, and rarely absent. 



^ Uuffmann, C. A'., Die Amphibian. Bronn's Classen und Orduuugen des Tliierreiclis, vol. VI. 

 pt. 2, 1873-78. — Wagner, J., Natiirliches System der Amphibieii, 1 828-33. 



