Carboniferous Coal Age. 85 



fingers besides a rudimentary thumb concealed under the skin. The 

 hind limbs have five digits. 



The Amphibian performs in his own person the passage of his ances- 

 tors, from the fish type to the reptilian type. 



The Labyrinthodont, mentioned above, constitutes an extinct order 

 of Amphibians that ranged from the Carboniferous into the Trias. It 

 was a frog with salamandriform body, weak limbs and long tail. Its 

 size was three feet long and two feet wide. On each of its limbs there 

 was a hand with four fingers and a thumb. It was partly covered with 

 bony scales over the body, and there were bony plates over the head. 

 It had strong jaws and conical teeth like those of the Ganoid fishes. A 

 cross-section of one of these teeth shows a remarkably complicated fold- 

 ing and plaiting of the dentine and enamel composing the tooth. The 

 same thing is observable in the tooth of the ganoid fish, except that the 

 convolutions are simple and comparatively plain. A great many species 

 of these animals have been found thirty-four species of seventeen 

 genera, in Ohio representing characteristics connecting them with the 

 ganoid fishes and with snakes, lizzards, and other reptiles. 



The coal producing era in America, was brought to an end not sud- 

 denly, however by the wrinkling up of the Appalachian ranges of 

 mountains. 



CHAPTER XII. 



MESOZOIC REPTILIAN AGE. 



The Mesozoic or Reptilian Age is divided into three periods in 

 Europe Triassic, Jurassic and Cretaceous. The names are retained in 

 America, but the first two are not very definitely separated. 



We still have in the Triassic advancing forms of conifers, also ferns, 

 and a new form of gymnosperm, the cycad, which had its forerunner in 

 Carboniferous times in the sigillaria. The Calami te and Lepidodendron 

 have disappeared. 



The Cycas was then sometimes thirty feet high. It still grows to 

 that size in the tropics. Another genus of cycads is the Zamia, which 

 occurs fossil and which still exists. It was ver}' short, not more than 

 three or four feet high and two or three feet in diameter. The cycad 

 family is the predominant plant during the Triassic and Jurassic 

 periods. No Grasses nor Mosses. 



Animal life shows change and progress. The Echinoderm Cystids 

 are gone, but there is a greater abundance of the Crinids, including the 

 beautiful lilly Kncrinitcs. As to the Ophalopods, the Orthocoras and 



