524 



MANUAL OF ZOOLOGY. 



have been apodal. Little is known, necessarily, of their de- 

 velopment, but the singular genus Archegosaurus possessed 

 permanent branchial arches, and was, therefore, apparently 

 perennibranchiate (if not truly a larval form), whilst its noto- 



Fig. 286. Section of the tooth of Labyrinthodon (Masto- Fig. 287. a Skull of Laby- 

 donsaurus) Jcegeri, showing the microscopic structure. rinthodon Jtegeri, much re- 

 Greatly enlarged. Trias. duced in size; b Tooth of the 



same. Trias. Wiirtemberg. 



chord was persistent, and simply had rings of osseous matter 

 deposited in it. 



As to their distribution in time, the Labyrinthodonts range 

 from the Carboniferous to the Trias, inclusive, being most 

 numerous in the former period, but attaining their maximum 

 in point of size in the latter. 



DISTRIBUTION OF AMPHIBIA IN TIME. From a geological 

 point of view, by far the most important of the Amphibia are 

 the Labyrinthodontia, the distribution of which has just been 

 spoken of. The living orders of Amphibia are of much more 

 modern date, being, with the exception of some not wholly 

 certain Urodelans, wholly Tertiary and Post - tertiary. The 

 Anoura are represented by both Toads and Frogs in Miocene 

 times, and they have survived to the present day. The 

 " Tailed " Amphibians are best known to geologists by a sin- 

 gular fossil, which was described by its original discoverer as 

 human, under the name of Homo diluvii testis. The fossil in 

 question is of Miocene age, and it is now known to belong to 

 a Salamander, nearly allied to the Giant-salamander of Java 

 ( Cryptobranchus). 



Geinitz has given the name of Palaosiren to a fossil Am- 



