LIFE IN PRIMARY PERIOD 237 



Many genera of Stegocephala are known, all belonging to 

 the Permian epoch. They were not very large, the largest, 

 Sphenosaurus, being about two metres in length, Archegosaurus 

 de Decken of the Permian of Germany measuring a metre and a 

 half, Chelydosanrus of the Permian of Bohemia about one metre, 

 and Actinodon of the Permian of Autun, which has been so 

 completely reconstructed by Albert Gaudry, a little less. 

 Euchirosaurus of the same region was a related form. All 

 these organisms had the general appearance of small Crocodiles 

 or large Lizards, but it has been established that the young 

 of Archegosaurus had branchial arches. The scales on the belly 

 of Chelygosaurus formed about forty bands " enchevron ", very 

 regularly and elegantly arranged, while the belly of Actinodon 

 was equally well protected. Some species such as Dinorophns 

 multicinctus of Texas had a carapace like that of the Chelonians 

 united to the vertebral skeleton, and for that reason Cope 

 called them Batrachian-armadillos. The Stereospondyles are 

 represented by analogous forms, Loxomma of the upper 

 Carboniferous of England and the Permian of Bohemia. They 

 really constitute an outpost which continued into the Trias, 

 when the structure of their teeth, characterized by sinuous 

 folds, has earned for them the name of Labyrinthodonta. The 

 Stegocephala, Temno- and Stereospondyles seem to have 

 belonged to the fauna of the North Atlantic continents. 



Even at this epoch, however, the true Reptiles had already 

 appeared, whose embryos no longer had anything but useless 

 rudiments of gills, and alone were born with a special 

 apparatus for aerial respiration. This advance seems to have 

 been made during the lower Permian period ; it seems to have 

 been first achieved in America by Eryops, whose skull 

 alone was six decimetres long and four decimetres wide, and 

 by Cricotus, which was almost four metres long. The bodies 

 of the vertebrae were still made up of three pairs of separate 

 parts in Eryops, while in Cricotus the neural arches were 

 united with posterior elements called interventrals, and the 

 basiventrals were united to each other, a condition which also 

 occurred in the former genus. This last character marks 

 the line of separation between the first Reptiles and the last 

 Batrachian Stegocephala. The transition between the two 

 groups is thus practically imperceptible. 1 



1 In the early Batrachians and in the embryos of the present forms during 

 the early phas s of their development, the vertebras are composed of two 



