LIMBLESS AMPHIBIANS. 



75 



displaying many signs of affinity with Reptiles, they resemble 

 Amphibia in having two condyles to the skull (when any are 

 present), and the vertebrae are of a simple type. The chest was 

 in many cases protected by a shield formed of three sculptured bony 

 plates, of which the middle one appears to represent the inter- 

 clavicle and the lateral pair the clavicles of other vertebrates. In 

 form they were mostly salamander-like. The order is divided into 



Fig. 75. 





The Skull of a Labyrinthodont (Mastodonsaurus giganteus), upper view with 

 sculpture omitted, from the Lower Keuper of Wiirtemberg ; about 

 one-eighth nat. size. Ep. lateral supratemporal : Fr. frontal ; Ju. jugal ; 

 L. lachrymal ; Mx. maxilla ; Na. nasal ; P. parietal ; Pr.f. prefrontal ; 

 Pt. postfrontal; Pt.o. postorbital ; Q.J. quadratojugal; S.T. prosqua- 

 mosal; S.Oc. inner supratemporal; Sq. squamosal. The double lines 

 indicate slime canals. 



four groups : (I.) Branchiosauria, typified by the minute Protriton, 

 or Branchiosaurus of the Permian : (II.) the snake-like Aistopoda, 

 of the Carboniferous and Permian ; (III.) Microsauria, represented 

 by Hijlonomus of the Carboniferous and Hyloplesion of the Permian, 

 both small forms approximating to the Rhynchocephalian Reptiles ; 

 and (IV.) Labyrinthodonta, which includes the larger forms, such as 

 Mastodonsaurus (fig. 75), Loxomma (572), and Rhytidosteus (573), and 

 ranges from the Upper Carboniferous to the Trias. Other specimens 

 exhibited are Brachyops (570) from India and Capitosaurus (571) 

 from England. 



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