THE PROGKESS OF LIFE 77 



present day represented only by Polypterus of the 

 rivers of Africa. A little later came the Actinop- 

 terygians, in which the paired fins are supported by 

 numerous radiating rays, as in the Acanthodii ; and in 

 the Carboniferous period they became common. All 

 the Deutozoic Teleostomi had cartilaginous skeletons, 

 enamelled scales, and either diphy cereal or hetero- 

 cercal tails. 



The Dipnoi, or lung-fish, breathe air as well as water. 

 Eemains of them have been found in Devonian rocks ; 

 but, as their teeth are the only hard parts of the 

 skeleton, very little is known about them. The 

 Coccosteidce, which lived from the Devonian to the 

 lower Carboniferous, are placed in the Dipnoi by Mr 

 A. Smith Woodward. They had the anterior portion 

 of the body protected by an armour of large plates, 

 like the Ostracodermi, but their paired fins are un- 

 known, and so could not have been armoured. They 

 had, however, well developed jaws and teeth. 



We will turn now to the land. 



The flora of the Devonian period shows a consider- 

 able advance on that of the Silurian. More than a 

 hundred species are known, including, probably, most 

 of the principal types of Cryptogams as well as true 

 Gymnosperms ; among the former being ferns and 

 Archceocalamites, as well as the large cryptogamic 

 trees, Lepidodendron and SigiUaria. 



Owing to the numerous excavations made in coal- 

 mining, we know the flora of the lowlands and 

 swamps of the Carboniferous period remarkably well ; 

 but it is practically the same as that of the Devonian, 

 and was continued with little alteration into the 



