312 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



breathers pass one stage beyond the cryptobranchs in the oblitera- 

 tion of the gill-aperture, date from the Eocene period, when forms 

 more or less nearly allied to recent types appear. Both Triton and 

 Salamandra are represented. Remains of tailless amphibians (Anu- 

 ra), more or less nearly allied to modern forms, have been obtained 

 from the Tertiary lignitic and fresh-water strata (Oligocene, Mio- 

 cene) of Western and Central Europe. Palaeobatrachus diluvianus, 

 one of the oldest known forms, is from the lignitic strata of Orsberg, 

 near Bonn, Germany. The lacustrine deposits of Oeningen have 

 yielded several extinct genera, among which are Latonia (related to 

 the Brazilian horned toad, Ceratophrys), Palaeophrynus (a bufonine 

 type), and Pelophilus, the last not impossibly a true Bombinator. 

 Among recent genera, Rana, Bufo, and Pipa have also Tertiary 

 representatives. 



The paucity of remains of existing types of amphibians, com- 

 bined with the circumstance of their very late appearance, renders 

 impracticable the determination of the phylogenetic relationships 

 which bind together the various groups. Equally uncertain are 

 the stages which mark the differentiation of the modern fauna 

 from that of the Palaeozoic and the early Mesozoic periods, nor is 

 it likely that any progress towards the solution of this problem 

 will be effected until the void which is caused by the almost total 

 absence of amphibian remains from the deposits of Jurassic and 

 Cretaceous age will have been in great part filled. 



That the animals in question are derived either in whole or in 

 part from the dipnoan type of fishes there is very little doubt, but 

 the immediate connecting link or links between their ichthyic pro- 

 genitors, whatever these may have been, and the earliest stego- 

 cephalic forms are still wanting. The apparently sudden disap- 

 pearance with the Triassic period of the largely represented order 

 which contained all, or very nearly all, the earlier forms of amphib- 

 ians, without leaving in the modern fauna any positive indications 

 of its former existence, is not a little surprising, but it appears not 

 unlikely that the coecilians, which in many points of structure 

 resemble the ophidian labyrinthodonts, represent at least a part of 

 this ancient stock. Again, by many geologists the crocodiles are 

 assumed to be the modified descendants of the true labyrintho- 

 donts. 



