AMPHIBIA. 



181 



last-mentioned organs are not only often very numerous, but 

 are of large size. The subjoined illustration (fig. 542) shows 

 the beautiful and complex structure of the teeth, from which 

 the name of the order is derived. 



j^ 





1. ':k I 



/^A^^^:\X,_i / 



!) V 



Fig. 542.— Section of the tooth of Lahyrintlwdon (Mas- Fig. 543.— a, Slvull of Laby- 



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

 Greatly enlarged. Trias. duced in size ; b, Tootli of the 



same. Trias, Wtirtemberg. 



As regards their general distribution in time, the Laby- 

 rinthodonts range from the Carboniferous rocks to the Lias ; 

 but some of the forms commonly included in this order may 

 perhaps belong elsewhere. One type of the Labyrinthodonts 

 is constituted by the singular genus Archcgosaums, and the 

 less known Ajyateon — both from the Carboniferous rocks. 

 Archegosaurus is remarkable in having the notochord per- 

 sistent, and in the possession of permanent branchial arches. 

 It has been made by Professor Owen the type of a separate 

 group, the GcmoccijJiala ; but it is probably an immature and 

 larval form. The occipital condyles, also, do not seem to 

 have been ossified in the Archegosauria. 



Of the Carboniferous Labyrinthodonts the most important 

 genera are Anthracosaurus, Fteroplax, Loxoiimia, Keraterpeton, 

 Pholidogaster, Ophiderpeton, Ichthyerpeton, Urocondylus, Lepter- 

 Ijeton, Baphetes, Bmiiceps, Dendrerpeton, Hyhrpeton, and Hylo- 

 normis ; though the affinities of some of these are more or 

 less doubtful. Most of the Carboniferous Labyrinthodonts 



