404 



PALAEOZOIC SYSTEM OF ROCKS. 



Very recently a large number (thirty-four species referable to seven- 

 teen genera) of small Amphibians have been brought to light by the 

 Ohio Survey, and described by Cope. These are all, or nearly all, Laby- 

 rinthodonts (Stegocephali, Cope). Some of them have the usual broad 

 heads of Amphibians, but a large number are remarkable for their 

 long, limbless, snake-like forms and pointed heads. These are evidently 

 among the lowest form of Amphibians, and have strong affinities also 

 with Ganoid fishes. Figs. 583 and 584 represent two of the Ohio Am- 

 phibians. 



Some General Observations on the Earliest Reptiles.— With the pos- 

 sible exception of the Eosaurus, all the reptiles of the Carboniferous 

 were Labyrinthodonts. They are so called on account of the extraordi- 

 nary labyrinthine structure of their teeth, produced by the intricate 

 infolding of the surface and of the cavity. The same structure is ob- 

 served in Ganoid teeth, but in a far less degree. The simple infold- 

 ings of Ganoids (Fig. 449, p. 

 342) become intricate in Laby- 

 rinthodonts (Fig. 585). 



The Labyrinthodonts were 



Fig. 584.— Tuditanus radiatus, x I (after Cope). Fig. 585.— Section of Tooth of a Labyrinthodont 



probably the most complete example of a connecting type which has 

 yet been discovered. First, they were true Amphibians in the strictest 

 sense, having all of them in the early stages of their life — some through- 

 out life — both lungs and gills, and thus connecting water-breathers 

 with air-breathers. Again, they were very different from the slimy- 

 skinned Amphibians of the present day, in being covered, at least 

 partly, with bony plates or scales over the body, and with closely-fitting 

 bony plates over the head. Again, they differed wholly from the pres- 

 ent Amphibians in having jaws thoroughly armed with very large and 

 powerful teeth, the structure of which is labyrinthine. All of these 

 characters connected them with Sauroid fishes which preceded them, 

 and the great Saurian reptiles which succeeded them. Finally, they 

 seemed to possess also characters connecting them with several orders 

 of subsequently-existing reptiles. In the Labyrinthodonts and Sauroid 



