402 



PALiEOZOIC SYSTEM OF ROCKS. 



along with another small species of reptile, a number of land-shells — 

 pupa, etc. (Fig. 539, p. 394), and a myriapod (Fig. 565, p. 397). The 

 Sigillaria possessed a thick, strong bark, which was more resistant of de- 

 composition than the cellular interior. Stumps of these trees are often 

 found, consisting only of coaly bark filled with sandstone, evidently de- 



Fig. 579. — Jaw of Dendrerpeton Acadeanum, and Section of 

 Tooth, enlarged (after Dawson). 



Fig. 580.— Section of Hollow Sigil- 

 laria Stump, filled with Sand- 

 stone (after Dawson). 



posited within the hollow. These sands are rich repositories of organic 

 remains. We can easily imagine the circumstances under which the 

 Dendrerpeton was preserved. A dead Sigillaria tree, rotted to the base 

 and only its hollow stump remaining, stood on the margin of a coal 

 -swamp ; river-floods filled the stump with sand ; in the stump lived and 

 perished a Dendrerpeton ; or else, more probably, the dead body of the 

 reptile, together with shells and other organic remains, was floated into 

 the hollow stump and buried there. This reptile was probably a Labyrin- 

 thodont, but with strong alliances with true reptiles, especially Lacertians. 

 3. Archegosaurus {Primordial Saurian). — In the Bavarian Coal- 

 measures has been found the almost perfect skeleton of a reptile, about 

 three and a half feet long, which combines in a remarkable degree the 

 characters of Amphibians with those of Ganoid Fishes. It seems to 

 have been a Labyrinthodont Amphibian, with general form and struct- 

 ure adapted for a purely aquatic life. It had, certainly in the early 

 stages of its life, probably throughout life, both gills and lungs, and 

 therefore, like all the Amphibians of the present day at this stage, or 

 like Perennibranchiate Amphibians throughout life, breathed both air 

 and water. The locomotive organs were paddles, adapted for swim- 

 ming, not for walking. The body was covered with imbricated ganoid 

 scales (Fig. 581, A), and the head with ganoid plates. The structure 



Fig. 581.— Archegosaurus. 



of the teeth (B) was also ganoid. The bodies of the vertebra? were 

 not ossified nor even cartilaginous, but retained the early embryonic, 

 fibrous condition of a notochord, It was apparently a connecting link 



